Yes, and I’ll post this publicly in case anyone else needs clarification!

Flats means you’ll get a simple colored drawing with little to no shading. I might throw in a simple overlay with quick cel shading for free if I think it looks better that way.

Full color is always carefully shaded, with more detail and time put into the image. I usually cel-shade and then airbrush over it to give a softer look! The entire image is a bit more polished, including the lineart. This contributes to the higher price.