If I could give you just one piece of color advice it would be to mix your colors. What? You already put your icing in a bowl and add food coloring and mix away? Great! Not what I'm talking about though. And since I have a special talent for complicating the most simple of all things.... I took a bunch of pictures and even made some graphics to explain this incredibly easy and quick thing. Ready?
Make your icing colors like you normally do. You can make purple using left over blue and red icing. Or purple coloring straight out of the bottle. Using all natural beet dye to make that purple? Sounds weird... but I'm cool with that too.
Once you have your icing all mixed up and ready to go, you're going to mix your colors with each other. You can drop little bits of each color into the other ones, or just mix your spoons around. You don't need a lot. In fact, if it is a light color, add very little of the dark colors. They go a long way. If it is a dark color though, you'll need a bit more of the lighter color to make a difference. For the record, I actually ended up mixing about twice as much of each of these colors as the picture shows. You want to mix just enough so that you notice a difference.
The top line of colors is my icing straight from the bottle. Americolor electric pink, yellow, and electric orange. You can see that both the pink and yellow are actually a little too blue for the orange. (Can you see how the pink almost looks purple-ish and the yellow almost looks green-ish when you look at them next to the orange? It's called comparative value. We can talk about that another time.) You may remember that you need to add the color on the opposite side of the wheel, which conveniently happens to be orange.... or you can just mix the three colors together and everything magically comes out right every single time.
Here is another view of the same colors without the shiny parts to distract you. You can see that the colors themselves didn't really change that much from top to bottom. Cover the bottom half with your hand. The colors look just fine, right? Now cover the top half with your hand. Are you surprised at how similar the colors look as a group? They make complete sense TOGETHER.
I could pretty much talk about why this works for the next hour of my life... but I will save you that misery and wish you a happy nearly weekend.