Thank you for another one of your lovely comments!
That's exactly what I did! ^^ First, I drew the bear and the fairy, then I took a wet brush without any color to dampen the background. (Water colours blend nicely when the paper is slightly
wet before you touch it with color.
Then I mixed a color tone out of a tiny amount of blue + green and a larger amount of black. I took a very wet brush and only a tiny amount of this color mix to paint all of the background in light gray.
When it was still wet, I took a slightly bigger amount of this color to paint the lowest layer of trees and bushes.
Then I added much green to my color mix and added the next layer, then another one in dark blue and another one in black. Finally, I added highlights with white chinese ink.
Luckily, I had some of the original blue/green/black-mix left after that, as this was the ground color for the bear. Then I let everything dry and then colored the rest ^^
I have no idea if I'm good at explaining
In case you'd like to try this yourself, I recommend using real watercolor paper (not the one for kids which you usually use at school, but the slightly heavier one for artists with a rough surface). Smooth, thin paper would dry too fast, so there's no chance to create any watery effects... I'm not sure what kind of paper you're usually using? It looks very smooth, but I could be mistaken ^^