I look for colors that are lightfast and of good quality for professionals. For students a balance of quality to investment lightfast colors.
I use Holbein, Winsor & Newton, M. Graham, and Daniel Smith professional brands. Certain colors are only made by one brand. Students can start with a set of Van Gogh or Cotman which are distinctly better than craft grade paint. I use various mediums to work with for increasing paint flow or masking.
Gum Arabic is the binder used in traditional watercolors and gouache. Add additional gum arabic to watercolors to increase their transparency and gloss, while extending drying time. Winsor and Newton Gum Arabic Solution