Don't people usually tell you which layer to color on? Or at least name their layers? If they don't, my only suggestion is to try a layer, and if it isn't the right one then undo the coloring and try again on a different layer. I'm pretty sure Ctrl+Z works in Oekaki but it's been awhile since I tried coloring anything in it.
So I may as well announce the good news here. I may be getting my laptop back as soon as Tuesday!

I might, no promises on this, but I might do something special to celebrate. Dunno what yet so I'm open to suggestions. Not a new species, but once I do have said laptop I will probably start experimenting with making some.