Oh man. Watercolors. Don't think it's easy, I have the exact same problem as you. Everything ends up being brown if I start mixing colors and my brushwork is just plain awful. That's why if I have to paint, I prefer something where I can work with layers. So I can first paint one layer and then wait for it to dry and then keep on painting, to avoid everything becoming fucking brown again. So much hate.
I dunno, maybe you would like to try acrylic paint. Dries fast and it's so thick you can easily cover mistakes with another layer. Mixing colors is an artform itself, man. Mix lemon yellow with ultramarine and you get this odd olive color, while mixing lemon yellow with the cooler Prussian blue gives you more vibrant greens, depending how much you use blue. Could either be lime or emerald or something.
I guess the hint is to look at the colors as you mix them. A cool red is going to have a bit of a pink/magenta/purple shade to it, so cool reds make for better purples when you mix it with warm blues. While the warm red is more of an orange shade and will thus obviously make for a better orange when mixing it with warm yellows, which also are more of an orange shade than the more green-ish cool lemon yellow.
But luckily being pissed at this stuff at least gives you a lot to rant to the tupper, huh.
