diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 8c029aa7..f4d26d7b 100755
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -36,6 +36,22 @@ jobs:
              ls -al .
              sudo apt install gnupg1
 
+      - name: start xvfb
+        run:
+          Xvfb :0 &
+
+      - name: initialize the X11 DISPLAY variable
+        run:
+          export DISPLAY=:0
+
+      - name: Install libraries
+        run: |
+          sudo apt update
+          sudo apt install libgtk2.0-0
+
+      - name: Test with Gradle
+        run: xvfb-run -s '-screen 0 1024x768x24' ./gradlew test
+
       - name: Publish package
         run: bash publish.sh
         env:
diff --git a/src/main/java/eu/mihosoft/vrl/v3d/CSG.java b/src/main/java/eu/mihosoft/vrl/v3d/CSG.java
index 1d74a14b..aa0dcb5a 100644
--- a/src/main/java/eu/mihosoft/vrl/v3d/CSG.java
+++ b/src/main/java/eu/mihosoft/vrl/v3d/CSG.java
@@ -1257,7 +1257,7 @@ public CSG difference(CSG csg) {
 	 * @return the csg
 	 */
 	private CSG _differenceCSGBoundsOpt(CSG csg) {
-		CSG a1 = this._differenceNoOpt(csg.getBounds().toCSG());
+		CSG a1 = this._differenceNoOpt(csg.getBounds().toCSG().setColor(csg.getColor()));
 		CSG a2 = this.intersect(csg.getBounds().toCSG());
 		CSG result = a2._differenceNoOpt(csg)._unionIntersectOpt(a1).optimization(getOptType());
 		if (getName().length() != 0 && csg.getName().length() != 0) {
diff --git a/src/test/java/eu/mihosoft/vrl/v3d/CSGTest.java b/src/test/java/eu/mihosoft/vrl/v3d/CSGTest.java
index b6a829aa..c3f17eba 100644
--- a/src/test/java/eu/mihosoft/vrl/v3d/CSGTest.java
+++ b/src/test/java/eu/mihosoft/vrl/v3d/CSGTest.java
@@ -29,7 +29,7 @@ public void setColor_OnUnionCSGShouldRetainColorsOnPolygons() {
                 .transformed(new Transform().translate(10, 0, 0));
 
         CSG union = cube1.union(cube2);
-        assertEquals(CSG.getDefaultColor(), union.getColor());
+        assertEquals("Expected the new object to get the color from the unioned object", Color.RED, union.getColor());
 
         union.getPolygons().forEach(polygon -> {
             boolean isLeftCube = polygon.getPoints().stream().allMatch(p -> p.x <= 5);
@@ -51,7 +51,7 @@ public void setColor_OnUnionedAndTriangulatedCSGShouldRetainColorsOnPolygons() {
                 .transformed(new Transform().translate(10, 0, 0));
 
         CSG union = cube1.union(cube2).triangulate();
-        assertEquals(CSG.getDefaultColor(), union.getColor());
+        assertEquals("Expected the new object to get the color from the unioned object", Color.RED, union.getColor());
 
         union.getPolygons().forEach(polygon -> {
             boolean isLeftCube = polygon.getPoints().stream().allMatch(p -> p.x <= 5);
@@ -86,7 +86,7 @@ public void setColor_OnUnionedCSGShouldChangeColorsOfAllPolygons() {
                 .transformed(new Transform().translate(10, 0, 0));
 
         CSG union = cube1.union(cube2);
-        assertEquals("Expected the new object to get the default color", CSG.getDefaultColor(), union.getColor());
+        assertEquals("Expected the new object to get the color from the unioned object", Color.RED, union.getColor());
 
         union.setColor(Color.BLUE);
         union.getPolygons().forEach(polygon -> {