Over three years ago I wrote a convoluted script that did change layer colors.*** 😮
It needs Pro...
It renames the original layer.
It makes a DXF with the relevant original-layer-name, giving it the specified color and imports the DXF file to make the new layer, with the original-name and the new color...
Then it reassigns every entity in the model [and also inside its definitions] that used the original-layer to this new-layer [with the original-name]...
The original-now-unused-layer-with-the-temp-name is now purged.
Ta-da... the objects appear to be on the same layer but it has the specified new color...
*** layer-color=.rb
http://sketchucation.com/forums/viewtopic.php?p=177016#p177016
It IS unbelievably clunky.
It does something that the API ought to do readily !
I'd only use it if I really had to 😲
H