White is a really important color in gouache, and I defaulted to Titanium White until I started reading some interesting opinions online about Zinc White. It seems that Titanium White is more opaque and better for highlights and stars and things, but Zinc White is supposed to be a better mixing colors – to make nicer pastels.
So I got myself a tube of Zinc White gouache and tested out pastels made from Titanium vs Zinc with all my gouache colors.