My stepkids haven't commented so much on makeup, but when I was newly married to my husband, there were a few comments about the way I dressed...and the way I set the table, the way I cooked and so on.
I feel kind of good about the fact that these kinds of comments were usually complimentary. It's tough to be the "new stepmom" and it was nice to hear my teen-aged stepkids make positive comments. From teenagers! Involving their new (possibly wicked) stepmom! There were lots of things I apparently "did wrong", but I felt appreciated for my style (and no, I wasn't all that stylish clothing-wise at all...) - hard to explain, but I guess I was just different and it was ok?
Kids (toddlers, teens or young adults) have *no idea* how much it means to a parent or step-parent to hear something good!