Color theory is easy just paint gray scale and your golden
But color theory is a real pain if you're red/green color blind .. Like me .
We have the newbie Challenges and we have Paint pal. Paint pal is kind of like pen pals , But a lot more fun and is open to anyone who wants to join in . Makes no difference if you a beginner or old hat to the game it allows you to have a deadline , come up with an ideal and see it through and all on the size of material that is the size of most old school post cards .
I am glad you mentioned spidering on that glass , On canvas you never really notice it but on hard surface it shows up and fast.
But that is why doing it on glass is the best and hardest way to learn . But if you can master it on glass you can paint anything .