Color Effects and What Not

I was wondering if anyone knew of a tutorial on color effects? I've been overlaying colors on my icons and gradients as well, but they're not coming out right for some reason. Tons of people are creating icons in this style and I always like to try new things so I just wanted to know if there was a tutorial out there or if anyone would be willing to write up a tutorial on how to use color overlays or just color in icons? The best example I can give you of what I'm talking about is icons by saava. She's really mastered the whole color layer in icons. Does anyone know what I'm talking about? Because I'm terrible at explaining things. Anyway, just wanted to know.

Thanks!