I'm on the hunt for a really nice brown & it hasn't been an easy task! You would think learning from grade school, "just mix the complements of the colors & it should work". Yeah, it's not that easy. I belong to a couple of dyer email lists and there is constant talk about achieving a nice brown.
I tried different color combinations on swatches & soon discovered if the dye powder was not a pure color then just about anything could happen.
Red & green? (my green leaned toward the blue side) so it made a really nice purple. I had another green that leaned toward the yellow side, those are the rust colors you see above.
Blue & orange? (didn't have pure orange, so I used scarlet & sun yellow-which makes a beautiful orange by the way) something with the scarlet, once it hit the blue dye, again, a really nice purple. (counting down and over, that is swatch number 7)
Yellow & purple? (that's those funky drabby olive swatches you see above)
I thought if you mixed half of each color you'd get brown. What I learned is to start with the lighter of the 2 colors and slowly add the dark color until you can achieve that certain shade you're after.
I have bought the straight from the container browns from Dharma and ProChem & even those gave very weird versions of brown. With those they tend to lean more toward that drabby olive color which can be a nice color, but not when you're wanting a deep chocolate brown.
I am very happy with how these swatches turned out & I think they're all beautiful colors (& I did keep track of the recipes for each of these so I can recreate them) however, I know I've barely scratched the surface in researching achieving that "just right" brown.