This link takes you to the blog of one of the Whimsy design team members who shows you how to colour white images with Copic markers. I am not a Copic girl but the lesson in how to colour is appropriate no matter what medium you are using.
https://tanglemousecards.blogspot.com/2018/09/a-whiter-shade-of-pale.html
Whimsy Stamps have started a Wednesday Workshop day that may prove to be very helpful in giving you ideas on how to use their stamps. Don't forget that if you want a stamp that I don't currently stock I can order it in for you.
Happy crafting,
Julie