I need to make cobalt blue gum paste for some flowers and a lighter shade for fondant.

I have access to Americolor: Royal Blue, Navy Blue, Sky Blue, Violet
Wilton: Delphinium blue, and Cornflower blue.

Many other colors as well, just wanted to start with those few

I really need to figure this out soon, surely someone has made this color before!

double post

Will this help--http://cakecentral.com/articles/54/how-to-color-your-icing

I would do small test batches using Royal blue

Try your Royal Blue until you get the intensity you want then add some black a tiny bit at a time until you get the color you want. Remember colors will dry darker. HTH!