Regarding your pic number 2:
I usually would make the black outline for all of the drawing in the cookie. Afterwards, make it dry for 30 mins or so in the dehydrator. Then I would fill the colour of one, skip the one that is right at it's side, continue filling the other one, skip the one next to it and so on. I would leave it dry in dehydrator, let's say 20 mins while i do another cookie. And then fill in the gaps (regarding spaces i skipped on purpose)
I don't know if i have been clear and helped you with your dought? If not, pls let me know!