Hi Ibrahim,
The Color Key gui was just added (so you would need to get a current daily build for that), and I have not yet written documentation.  However, if you get it, it may be mostly self-explanatory.  Start from menu: Tools... Depiction... Color Key.

The command version was added earlier, a few weeks ago, and it has documentation as well as an example in the tutorial (linked to the image in the documentation):
<https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Frbvi.ucsf.edu%2Fchimerax%2Fdocs%2Fuser%2Fcommands%2Fkey.html&amp;data=04%7C01%7Cria2%40psu.edu%7C0476452bab254a86618d08d8e7e8d130%7C7cf48d453ddb4389a9c1c115526eb52e%7C0%7C0%7C637514334414685859%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=3NVuliTRhasmxxeSKDlUeQPDT7Lw7kORqqh4dfJA7ug%3D&amp;reserved=0>

I hope this helps,
Elaine
-----
Elaine C. Meng, Ph.D.                      
UCSF Chimera(X) team
Department of Pharmaceutical Chemistry
University of California, San Francisco

> On Mar 15, 2021, at 12:14 PM, Moustafa, Ibrahim M. <ria2@psu.edu> wrote:
>
> Hi Tom,
>   Another related question:
>   How to create a key for the color radial?
>   Thank you,
>   Ibrahim