The colors do not come out as bright. Basically you are mixing a tan (the egg) with whatever color you are using. Green will turn olive, orange is more of a copper color etc. If you keep that in mind, you can get nice effects.
I decorate eggs using all different ways.
I use magic marker, ukrainian dye method (batik), cut small pictures out and glue them on, use yarn, ribbon, watercolors, pen and ink, model paint, natural dyes, wrap leaf around egg with nylon and dye it in dye bath, food coloring, store bought egg colors, and more that I cannot think of at the moment.
One year we wrapped rubber bands around the eggs and died them. My stepson had lots of fun with that one.