Please help. Im making cupcakes for a very special birthday. I would like to know how to make dark blue and maroon icing, and what coloring works best. I find that when I try to darken the icing, it turns runny...thanks

Depends on what kind of food colouring you are using I use the paste, it helps keeps the icing's consistency the way you want it to be
if you mean by dark blue: navy??... try adding color portions as follow: 1 blue, 1 black, 1/2 purple
I never tried making Maroon but I read its 1 red & 1/2 burgandy
this site might help

www.baking911.com/decorating/tinting.htm

You definitely need to use gel food coloring Americolor if you have time to order or there is a cake supply store near you; otherwise Wilton gel colors are available at AC Moore, Micheals, Walmart, etc.