I don't know if I've ever tried putting creme makeup on top of the scar. Eyebrow pencil, yes, but not creme. All I can say is, experiment and let us know how it goes!
I regularly use rigid collodion for my Shuuhei and Luffy scars, and just darken them with a little brown eyebrow pencil. Not that I don't have a bajillion creme makeups I could test, it was just faster and easier to grab an eyebrow pencil and draw on top of the dried scar.
Founder and President, Madison Area Costuming Society, a chapter of the International Costumer's Guild
Strange Land Costuming - www.strangelandcostumes.com