Fixes area overlays being additive when using blueprints or admin bui…

…ldmode (#37118)

* area overlays blend mode fix for blueprints and buildmode

* it's not the blend mode you dummy, it's the plane!

code/game/objects/items/blueprints.dm

@@ -335,6 +335,7 @@ these cannot rename rooms that are in by default BUT can rename rooms that are c
 
 	//Create a visual effect over the edited area
 	edited_overlay = image('icons/turf/areas.dmi', currently_edited, "yellow")
+	edited_overlay.plane = ABOVE_LIGHTING_PLANE
 	editor.client.images.Add(edited_overlay)
 
 	to_chat(editor, "<span class='info'>In this mode, you can add or modify tiles to the [currently_edited] area. When you're done, bring up the blueprints or leave the area.</span>")

code/modules/admin/buildmode.dm

@@ -184,6 +184,7 @@ var/global/list/obj/effect/bmode/buildholder/buildmodeholders = list()
 /obj/effect/bmode/buildmode/New()
 	..()
 	area_overlay = image('icons/turf/areas.dmi', "yellow")
+	area_overlay.plane = ABOVE_LIGHTING_PLANE
 
 /obj/effect/bmode/buildmode/Destroy()
 	copycat = null