There are separate palettes for different things - one for armors, one for frame, one for weapons etc.
Basically select custom color first (usually white), edit it later, so it would display changes in real time.
It's super finicky, but it works and gives you huge amount of freedom.

1. Select style
https://cs2bus.com/sharedfiles/filedetails/?id=1703666956
2. Choose new custom style
https://cs2bus.com/sharedfiles/filedetails/?id=1703667009
3. Edit style
https://cs2bus.com/sharedfiles/filedetails/?id=1703667051
4. In edit window select previously chosen style in drop down menu.
This is the most confusing part
https://cs2bus.com/sharedfiles/filedetails/?id=1703667082
5. Edit your stuff
https://cs2bus.com/sharedfiles/filedetails/?id=1703667115
6. This fist of mine is burning red
https://cs2bus.com/sharedfiles/filedetails/?id=1703667151