The water-colouring process included two steps: edging around the outside of each flower in a chocolate chip reinker wash and wet into wet painting with two aqua painters (light wash and darker tone in craft ink for saturation of colour). The brown centers were easiest to do. I found that I could just slop on a circle of wash and go back in with darker tones, since I'd be trimming anyway.
EDITED TO ADD: More details
I use an aqua painter and reinkers. These primas were done in combos of: tempting turquoise & not quite navy (with chocolate chip centers); bordering blue & blue bayou; bordering blue & ballet blue.
I do several whole sheets of cardstock at once that way painting is faster (and I don't have to wait for them to dry between steps (I'm so impatient!).
First, I go around the edge with a light brown wash, then let it dry. After that, I use a wet into wet technique: just paint the flower quickly with a light wash of blue (sometimes twice depending on how quick it seems to be drying: you want it wet enough) then I go in with the dark ink in spots. It's fun when it bleeds into the light colour.
Then, yup (the tedious part) I cut them all out, BUT thankfully I just sent my paper snips out for sharpening (and with a wash around the outside you don't have to worry about perfection). Also this is a doodley set, so it's forgiving).