So I have never done any of the water color style painting on cakes but I have seen it done and I think its beautiful.
I absolutely love the Edgar Allen Poe themed cake they did on Ace of cakes, I am in awe.

one thing I have always wondered is what "paints" /dyes, colorings, do people typically use for this? I know you can water down gel color, Ive done that for small pieces before,but never entire designs on cakes. I have seen some where they paint on dark fondant, what gives the vibrant colors, like on that cake used a bright white..
Does any one know?

TIA

No idea, but bump-bump-bump... I'd love to know as well.

I've used airbrush colors to paint on cakes. I haven't done water color style of painting, but I like the airbrush colors cause they are already thin. You can see my 'painting' on the skate board cake in my photos.

I use the vodka method to paint on fondant. I have a little dish of vodka on the side of my work surface that I dip my paintbrush into the vodka and mix on a plate, I use it like a paint pallet with the gel icing colors. I also like to play with affects of different colored fondant. I would love to try airbrushing though it seems really nifty.
For little added effects I "airbrush" with luster dust. Before I take the cap off the little "tube" I shake it and flip it over once. Then I remove the lid and hold it flipped over in my fingers. I position myself in front of the cake where I want to add the detail, with the lid in between me and the cake. Hold it about 4 inches away from the cake and blow gently over the lid the moving air lifts the luster dust off the lid and it lands on the cake and sticks.
Good luck and have fun!

I use the Americolors, and they do have a white color as well. I bought a big bottle of it cause you can use it to lighten up other colors if they are too dark for you.

Welcome.