I seem to have a real problem with getting the right shade I want. 
For example when I want I very pretty light pink I don't know if I should use Rose, Pink, or mix them. I always seem to have to much purple in it or it looks to peachy. I have the same problem with blues. The color that Wilton has on their bottles is never the color I end up with. 
Another thing is that when I get a nice color and want a contrasting light or dark shade of the same color I can't seem to get it. I put in more of the same gel or use the white to lighten but it looks like a totally different color. Is there a chart that shows every color and what to mix to get that color?I don't know why I have so much problem with this since I did a lot of painting before I started doing cakes. I guess since I can't actually see what color the gel is in the bottle that I have a hard time visualizing how it will be once it is mixed. I hope someone knows of a chart like this because it would really help me out.
http://www.wilton.com/cake/icing/colorchart.cfm
That's the wilton color chart. Don't know what to tell you about blue - mine always comes out true to form.
As far as pink goes, if you're not happy with the colors you're getting, try using just the tiniest dab of red. That's usually how I make my pink.
I gave up Wilton colors a long long time ago! I use nothing but Americolor!!!!! Always start out with the tiniest amount. One thing to remember when you color your icing, the color will ALWAYS darken after it sits for a while.
I'd love to see some of your paintings but I know you can't post them here ! 
Amy
I totally agree with the others on using Americolor! I color my icing a little bit lighter than what I actually need. And, I try to make my icing at least 1 day in advance, to give the color time to darken. 
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