The tutorial of how I achieve watercolor effect in Sai! :) I highly recommend using real watercolor paintings (your own or ones found on the internet) as reference.

And here you can find a few useful links: 

  1. You can download the Sai file of this picture here: link 
  2. Video process of painting another picture: link
  3. The old watercolor tutorial: link
  4. Sai brushes (none of them is made by me) link + file you need to open them in Sai: link
  5. Awesome watercolor brushes made by Kyle T Webster: link

Here’s the finished painting: link

From the developer’s website
” RefBoard is a simple, lightweight image viewer designed with artists in mind. Display as many referance images as you need simultaniously and over any windowed application! RefBoard also features a discrete UI that stays out of the way, is completely scalable, supports drag and drop and is 100% free! “

I found this program thanks to a review in ImagineFX magazine. It’s super minimal, but it seems so useful for looking at your reference images while painting without storing them in the file that you’re painting or trying to negotiate with multiple PS windows!