Gave it a whirl, is there anyway to avoid all that color bounce when you use the brush? Well as far as painting on top of things anyway. I kept getting all these weird colors when I decided I wanted to change the saturation of the color I was already using. Other than that I like how smooth it is
Figured out the shenanigans that were going on, I had the brush set to vivid so it was mucking things up to Nth degree. Totally diggin on Sai though. It's like what I dreamed Open Canvas would be like only smoother and more functional
Here's something that worked for me. Keeping the longs on a separate layer, you can turn on 'preserve transparency." With that on, you can paint the lines a different color to match the layer under it, add subtle lines or highlights, and ultimately blend it in. Afterward, turn off preserve transparency and erase the excess lines. Merge layers, paint over them a little bit, and done. Pretty quick, simple, and it looks great!