I went to a sale at Zart Art late last year and there was a man demonstrating using watercolour paints and black pen for an art activity in the classroom.
I remembered it recently and did the preliminary work. I had got out my watercolour crayons and just put some lines on paper and then swished some water around.
I experimented by wetting some areas of the paper and not others. The crayons just did fairly ordinary straight lines where the paper was wet. When I put the crayon on the dry paper, and then swished water around with a brush, the colours mixed nicely and the obvious pencil marks disappeared. But overall, the thing looked like a mess.
Unfortunately, I didn't take a photo.
Then, over the next few days, I did a little bit of doodling with a black pen. I went around the areas of different colours and intensity.
I quite like the result. I have no idea what to do with it now. I suppose I should treat it like the zen doodles, just let myself enjoy the process, not worry about the end product.