I'm new to cake decorating, so this question may be really dumb, but...
I have the worst time coloring my icing. I often see people talk about how they match colors of their icing from a party invitation or something and it baffles me! I can't even make the icing match the vision I have in my head! I use the little jars of Wilton gel coloring and toothpicks (as I was taught in class one). It seems to take FOREVER and never comes out the way I want.
So, what is the best way to color icing?
Thanks! 
I would say practice and more practice. The more you do, you get a better feel for what you can achieve. It really is sort of a feel. There is a color "cheat sheet" floating around in one of the threads...maybe someone has a quick link to it.
The best advice I have is to start by adding color slowly - you can always add more but you can't really backtrack when it is too dark or is going a direction you don't want/like.
Oh - another thought. Have you ever tried Americolor gel color? You can order them right here on CC, on other sites online or some decorating supply stores have them. They come in little flip top bottles and you can squeeze in a drop of color or more, depending on what you need. No more messy toothpicks. They are GREAT! (especially the super red and super black - I think far superior to the Wilton gels).
awolf24, you beat me to it. I was going to say that the first thing to do is throw out the Wilton colors and go to Americolor! 
Diane
awolf24...is this the "cheat sheet" you were talking about?
http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=858073
Hope it helps!
Coloring buttercream is very hard. They always tend to darken after they're put on the cake. I would say if it is something that you absolutely have to match then play around with the icing a few days early.
For instance, put about 1/8 - 1/4 cup icing in a bowl. Add a little color. Then smear a little dab of that, about 1/2 tsp., on the inside top of the bowl. Add a little more color. Smear some of it on the bowl next to the one you previously did. Repeat this process until you have about 5-7 smears on your bowl. Let it air dry a few days.
Then pick the "smear" that best matches the color you want. Then break open the one you want you'll see the color that you need to make. It will be lighter. That color will be your goal. Then you can color the whole batch and not worry about wasting it. Once it's on the cake it should come out as the color you want.
That seems like a lot of work but I ONLY do that if I'm trying to perfectly match a color. Plus it gives you a chance to see how different colors react.
As was stated in another post, you just have to practice. Eventually you'll learn how the colors work. It just takes time.
Oh, and to throw another kink in it all ~ gumpaste tends to get lighter the longer it sits 
Have Fun
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