You are being too worried with the end result: A full color design.
Iīve read a couple times about the 1000 or maybe 10000 hours theory: You only will learn after having practicing this amount of time.
My suggestion is draw in pencil 10 drawings. Then get the best ones and post. Get some feedback and do it again.
Donīt waste your time trying to paint them now.
Maybe do one month just drawing and ask feedback of them, then after that do one month painting your best drawings (get feedback of your painting). After that start over again...you will see progress. Donīt start from the end.
You already got more feedback than most people get. Use it! Good luck