Yasmeen is an illustrator and colorist. On her YouTube channel for her YamPuff brand of coloring books you will find flip throughs of her books. There are also tutorials featuring speed coloring in both pencils and markers.
Yvonne Döring hasn’t uploaded videos for a while but you can still learn a lot from the ones on her channel. You will find speed coloring in Johanna Basford books, Kerby Rosanes, Hannah Lynn, and more.