I agree with the above post that you may be overblending when doing smokeys involving browns (esp. darker richer browns).
It helps to have a light neutral base all over your lid (with shimmer, preferably, as I find that aids the blending process) - when you apply your darkest brown (or crease color), only pat/dab a little bit at a time (while depositing most of the color near the lash line) and then try blending using a blending brush (like 217) in small circles outwards, GENTLY. If you find the crease color to be not dark enough still, then add a little more. I remember when I started experimenting with smokey browns, I often put too much dark crease color on, then tried desparately to blend it to perfection, which always resulted in a bloody, muddy mess.
Also, do not overblend between each color on your eyes (i.e. between a lighter and darker color) - only blend using small vertical strokes between each color until the harsh lines are softened (so you get a slight gradient between the colors) - when you overblend between each color, the result is also a muddy mess lol.
One last thing is to try avoid bringing the darkest shades too much into lighter ones, this also causes the muddy look (so always gently blend the lighter shades into the darker ones, and not vice versa).
Good luck!