Using any color you like as long as you can see the line art, create a layer to make color layers easier to work with.

I picked a color that I won't really be using much in the actual drawing, although since this drawing is going to be mostly black and white anyway, I could have picked any color! ＼（＾▽＾）／ Anyway, now we have this color.

layer 1

line art

background