diff --git a/src/languages/colour.ts b/src/languages/colour.ts
index a6270b075..640f5b8f4 100644
--- a/src/languages/colour.ts
+++ b/src/languages/colour.ts
@@ -9,16 +9,10 @@ export function initialiseColourChecker(context: ExtensionContext) {
     workspace.onDidOpenTextDocument(async (document) => {
       if (document.uri.scheme === `member` && !document.isClosed) {
         const content = document.getText();
-        let hasInvalidCharacters = false;
-        for (let i = 0; i < content.length; i++) {
-          if (replaceCharCode(content.charCodeAt(i))) {
-            hasInvalidCharacters = true;
-            break;
-          }
-        }
+        let doWork = hasInvalidCharacters(content);
 
-        if (hasInvalidCharacters) {
-          const shouldFix = await shouldInitiateCleanup();
+        if (doWork) {
+          const shouldFix = await askUserToStart();
 
           if (shouldFix) {
             const fixedContent = replaceInvalidCharacters(content);
@@ -32,14 +26,23 @@ export function initialiseColourChecker(context: ExtensionContext) {
   )
 }
 
-function replaceCharCode(charCode: number) {
+export function hasInvalidCharacters(content: string) {
+  for (let i = 0; i < content.length; i++) {
+    if (shouldReplaceCharCode(content.charCodeAt(i))) {
+      return true;
+    }
+  }
+  return false;
+}
+
+function shouldReplaceCharCode(charCode: number) {
   if ((charCode < 32 && !NEW_LINE_NUMBERS.includes(charCode)) || (charCode >= 128 && charCode <= 157)) {
     return true;
   }
   return false;
 }
 
-async function shouldInitiateCleanup() {
+async function askUserToStart() {
   const config = instance.getConfig()
 
   if (config?.autoFixInvalidCharacters) {
@@ -65,12 +68,12 @@ async function shouldInitiateCleanup() {
   return true;
 }
 
-function replaceInvalidCharacters(content: string) {
+export function replaceInvalidCharacters(content: string) {
   const chars = content.split(``);
 
   // return content.replace(/[\x00-\x1F]/g, ``); // This almost works, but we want to keep line feed / carriage return
   for (let i = 0; i < content.length; i++) {
-    if (replaceCharCode(content.charCodeAt(i))) {
+    if (shouldReplaceCharCode(content.charCodeAt(i))) {
       chars[i] = ` `;
     }
   }
diff --git a/src/testing/encoding.ts b/src/testing/encoding.ts
index fe3fa8083..3da5c0f70 100644
--- a/src/testing/encoding.ts
+++ b/src/testing/encoding.ts
@@ -7,6 +7,7 @@ import { Tools } from "../api/Tools";
 import { instance } from "../instantiate";
 import { CommandResult } from "../typings";
 import { getMemberUri } from "../filesystems/qsys/QSysFs";
+import { hasInvalidCharacters, replaceInvalidCharacters } from "../languages/colour";
 
 const contents = {
   '37': [`Hello world`],
@@ -27,43 +28,100 @@ export const EncodingSuite: TestSuite = {
     assert.ok(config.enableSourceDates, `Source dates must be enabled for this test.`);
   },
 
-  tests: Object.keys(contents).map(ccsid => {
-    return {
-      name: `Encoding ${ccsid}`, test: async () => {
-        const connection = instance.getConnection();
-        const config = instance.getConfig()!;
+  tests: [
+    ...Object.keys(contents).map(ccsid => {
+      return {
+        name: `Encoding ${ccsid}`, test: async () => {
+          const connection = instance.getConnection();
+          const config = instance.getConfig()!;
 
-        const oldLines = contents[ccsid as keyof typeof contents];
-        const lines = oldLines.join(`\n`);
+          const oldLines = contents[ccsid as keyof typeof contents];
+          const lines = oldLines.join(`\n`);
 
-        const tempLib = config!.tempLibrary;
+          const tempLib = config!.tempLibrary;
 
-        const file = `TEST${ccsid}`;
+          const file = `TEST${ccsid}`;
 
-        await connection!.runCommand({ command: `CRTSRCPF FILE(${tempLib}/${file}) RCDLEN(112) CCSID(${ccsid})`, noLibList: true });
-        await connection!.runCommand({ command: `ADDPFM FILE(${tempLib}/${file}) MBR(THEMEMBER) SRCTYPE(TXT)`, noLibList: true });
+          await connection!.runCommand({ command: `CRTSRCPF FILE(${tempLib}/${file}) RCDLEN(112) CCSID(${ccsid})`, noLibList: true });
+          await connection!.runCommand({ command: `ADDPFM FILE(${tempLib}/${file}) MBR(THEMEMBER) SRCTYPE(TXT)`, noLibList: true });
 
-        const theBadOneUri = getMemberUri({ library: tempLib, file, name: `THEMEMBER`, extension: `TXT` });
+          const theBadOneUri = getMemberUri({ library: tempLib, file, name: `THEMEMBER`, extension: `TXT` });
 
-        await workspace.fs.readFile(theBadOneUri);
+          await workspace.fs.readFile(theBadOneUri);
 
-        await workspace.fs.writeFile(theBadOneUri, Buffer.from(lines, `utf8`));
+          await workspace.fs.writeFile(theBadOneUri, Buffer.from(lines, `utf8`));
 
-        const memberContentBuf = await workspace.fs.readFile(theBadOneUri);
-        let fileContent = new TextDecoder().decode(memberContentBuf);
-        
-        if (rtlEncodings.includes(ccsid)) {
-          const newLines = fileContent.split(`\n`);
-          
-          assert.strictEqual(newLines.length, 2);
-          assert.ok(newLines[1].startsWith(` `)); // RTL
+          const memberContentBuf = await workspace.fs.readFile(theBadOneUri);
+          let fileContent = new TextDecoder().decode(memberContentBuf);
 
-          assert.strictEqual(newLines[0].trim(), oldLines[0]);
-          assert.strictEqual(newLines[1].trim(), oldLines[1]);
-        } else {
-          assert.deepStrictEqual(fileContent, lines);
+          if (rtlEncodings.includes(ccsid)) {
+            const newLines = fileContent.split(`\n`);
+
+            assert.strictEqual(newLines.length, 2);
+            assert.ok(newLines[1].startsWith(` `)); // RTL
+
+            assert.strictEqual(newLines[0].trim(), oldLines[0]);
+            assert.strictEqual(newLines[1].trim(), oldLines[1]);
+          } else {
+            assert.deepStrictEqual(fileContent, lines);
+          }
         }
       }
-    }
-  })
+    }),
+    {name: `Colour fix test`, test: async () => {
+      const connection = instance.getConnection();
+      const config = instance.getConfig()!;
+
+      const tempLib = config!.tempLibrary;
+      const file = `COLOURS`;
+      const member = `THEMEMBER`;
+      
+      await connection!.runCommand({ command: `CRTSRCPF FILE(${tempLib}/${file}) RCDLEN(112)`, noLibList: true });
+      await connection!.runCommand({ command: `ADDPFM FILE(${tempLib}/${file}) MBR(${member}) SRCTYPE(TXT)`, noLibList: true });
+
+      const aliasName = `${tempLib}.test_${file}_${member}`;
+      await connection?.runSQL(`CREATE OR REPLACE ALIAS ${aliasName} for "${tempLib}"."${file}"("${member}")`);
+
+      try {
+        await connection?.runSQL(`delete from ${aliasName}`);
+      } catch (e) {}
+
+      const lines = [
+        `insert into ${aliasName} (srcseq, srcdat, srcdta)`,
+        `values `,
+        `  (01.00, 240805, '      // This illustrates 5250 attribute bytes.'),`,
+        `  (02.00, 240805, '     '),`,
+        // `--(05.00, 240805, '     C*' concat x'XX' concat 'X''XX''' concat x'404020' concat  'X''XX'' GRN RI UL BL CS ND'),`,
+        `  (03.00, 240805, '     C*' concat x'20' concat 'X''20''' concat x'404020' concat  'X''20'' GRN               '),`,
+        `  (04.00, 240805, '     C*' concat x'24' concat 'X''24''' concat x'404020' concat  'X''24'' GRN    UL         '),`,
+        `  (05.00, 240805, '     C*' concat x'25' concat 'X''25''' concat x'404020' concat  'X''25'' GRN RI UL         '),`,
+        `  (06.00, 240805, '     C*' concat x'2E' concat 'X''2E''' concat x'404020' concat  'X''2E'' RED    UL BL      '),`,
+        `  (07.00, 240805, '     C*' concat x'2F' concat 'X''2F''' concat x'404020' concat  'X''2F'' RED             ND'),`,
+        `  (08.00, 240805, '     C*' concat x'30' concat 'X''30''' concat x'404020' concat  'X''30'' TRQ          CS   '),`,
+        `  (09.00, 240805, '     C*' concat x'36' concat 'X''36''' concat x'404020' concat  'X''36'' YLW          CS   '),`,
+        `  (10.00, 240805, '     C*' concat x'37' concat 'X''37''' concat x'404020' concat  'X''37'' YLW          CS ND'),`,
+        `  (11.00, 240805, '     C*' concat x'3D' concat 'X''3D''' concat x'404020' concat  'X''3D'' PNK RI UL         '),`,
+        `  (12.00, 240805, '     C*' concat x'3E' concat 'X''3E''' concat x'404020' concat  'X''3E'' BLU    UL         '),`,
+        `  (13.00, 240805, '     C*' concat x'3F' concat 'X''3F''' concat x'404020' concat  'X''3F'' revert to default '),`,
+        `  (14.00, 240805, '     '),`,
+        `  (15.00, 240805, '       *inlr = *on;'),`,
+        `  (16.00, 240805, '       return;')`,
+      ];
+
+      await connection?.runSQL(lines.join(` `));
+
+      const theBadOneUri = getMemberUri({ library: tempLib, file, name: member, extension: `TXT` });
+
+      const memberContentBuf = await workspace.fs.readFile(theBadOneUri);
+      const fileContent = new TextDecoder().decode(memberContentBuf);
+
+      assert.ok(hasInvalidCharacters(fileContent));
+
+      const newContent = replaceInvalidCharacters(fileContent);
+
+      assert.notStrictEqual(newContent, fileContent);
+
+      assert.ok(hasInvalidCharacters(newContent));
+    }}
+  ]
 };