I've been having that issue lately as well, the powdery issue. No problems with drying or lumpiness. Sugarbelle suggested it is from beating too long. I barely beat so it can't be that. I interchangeably use different brands of powdered sugar, thought it may be that issue so I experimented. Nope, it's happening with both brands. Soooooooo....what is it? I used different brands of color, always have. It's just a recent problem for me so I'm stumped. I live in the central US, use egg whites, no meringue powder and I shoot for about a 6 second-icing, which I use to both outline and flood. What I have been doing differently, somewhat so, is making larger batches at a time. I'm going to make 4 separate batches today and see if I get any noticeable difference. Will post results.