Hi @albert ,
There are several options for the colorization of structures or visual models (Ribbons is a visual model) based on chains:
The colorization using color schemes. First, select the Ribbons visual model in the Document view that you would like to colorize. Then: Biology > Colorize > Chain ID or Chain (illustrative) (i.e. in the style of D.S.Goodsell)aedf2d1e-77e3-42cd-af72-51400ba6f73b-image.png
You can also choose "Custom..." from the list and specify the color palette. The colorization with constant colors per chain. Choose a chain in the Document view. Set the color using Visualization > Colorize.
See more in User guide - Colorizing and User guide - Visualizing.