How to clean a speck case for iPhone?

My pink case was bright pink up until yesterday and now it looks like dust got on it from yesterday when I went to the mountains. How do I clean it to get it back to its original look? I tried a towel and a bit of water but it didn't remove all the dirt.

Use a hair dryer at minimum hot, 6 inches away, and clean it simultaneously with soft cotton cloth or hanky, using chemical will destroy the color.