You can do this without a macro, click the drop down next to the selection arrow for power select. There you will find select by color. you can even do this after a draft analysis to pick those faces.
If I have a model on which the faces are different colours, will this allow me to select a group of colours and offset a certain amount?
power select will get you the collection of surface selected - then start whatever command you wish (such as offset surface)
wait I just re-read your post, I think it will only do one color at a time...
- click the drop down next to the selection arrow in the toolbar.
- check "Pick color from graphics"
- click a face on the model that is the color you want to select.
- click search, it will select all the faces that match that color,
- click close
- click the offset surface while the surfaces are still selected