Playing around with the Pentel Aquash Pen with light black ink and gouache (Lukas) on Stonehenge Kraft (if you are going to bind with this paper please read my post about the difficulties before you do).
I've used up most of my Lukas gouache, which is not a fine art gouache, but is fun to use in my journal. And it's really very opaque. I've been having so much fun with it that I'm actually considering ordering up another set (I think there are 12 colors) for about $30 from ASW (My local store doesn't carry this line.)
Specifics about Lukas Gouache because I know someone will ask:
Negatives: The pigments aren't labeled; cost would lead one to believe they use inexpensive pigments; the muddiness of some color mixing would indicate a lot of two- or more pigment paints; slight chemical smell I'm not fond of but can live with (probably also indicates additives I don't have in my art quality paints and would explain some more of the muddiness).
Positives: Inexpensive and useful for quick studies in my journal, or for goofing around with when I don't want to get expensive paint out and "take time." Nice and thick, with a good body. Opaque. Fun to use thickly with dry-brush techniques because it is (didn't I mention this) so inexpensive.
I would not recommend Lukas gouache for someone interested in learning color theory and using gouache to mix colors. It's just a fun to use, inexpensive paint.