Advice from an over-the-hill artist XD (not that I'm an expert/good artist, just something I've learned): Are you coloring directly on your sketchbook pages? If you are, I REALLY recommend two things: a lightbox and thicker paper (Bristol board, etc.) It has been a game-changer for me to use the lightbox to "trace" my art onto the thicker paper and color a "clean" image on the thick paper. So, tape your sketchbook page with your sketch onto the lightbox, then tape the thicker paper on top. Ink "trace" the lineart of your sketch onto the thicker paper (Or, if you don't want to ink, use a black colored pencil to trace your lineart.) Then, pull off the thick paper (with the super clean lineart on it!) and color that! That has made me SO much happier with my art as I'm not smudging anything or dealing with "bleeds" because I'm coloring directly onto (thin) sketchbook paper with markers. Plus, there's no sketch-line eraser smears or divot-lines to deal with~!