you can convert RGB to HSL/HSL to RGB. summing colors would be easy with some basic math. you can just sum 2 R(or G or B) values and cap it to 255. or map it 510 (not sure which one to use).
summing %s is almost same thing. but calculate with % values.
(if values are between 0 and 1. no difference in math tbh)
Jens reminds me that if you make a one-pixel costume with the color you want, it displays in speech balloons just like a color -- a square filled with the color in question. I'm now working on using that to extend the Colors and Crayons library for first class colors.
I made a prototype: ProjectName=firstclass-colors @sathvikrias what other blocks do you need?
The mix colors block doesn't really work very well but the rest of it does.
Edit: Oh, I just made a minor mistake that's easily fixed. Never mind. The mix colors block s working now.