And, for anyone who suddenly finds they cannot use AP flour because of gluten or wheat intolerance, what's a person to do when they need roux?
Rice flours, for some reason, just don't brown well once mixed with the fat. They lump and clump and generally look melatonin-challenged.
But, browning the flour dry, as suggested by crrush, works extremely well. You can get it as dark as you want (either in the oven or on the stove in a pan) and then add the fat.
A good rule of thumb when substituting for AP flour is that a mix of GF flours works best - some sweet rice, some white or brown rice, and some potato starch maybe.