This was done with Derwent Inktense pencils, but I then used the idea with my class of 10 years. Unfortunately their pieces of art and the numerous other examples I completed are at school. It was a fun way to work on colour theory with them. I only had the one small sample I had done with the school watercolours, mixing to secondary and then tertiary colours.
This is an entry in PaperArtsy - Colour Mixing Challenge.