Ok I know this is going to sound basic and "elementary" but I'm literally tired at the moment. I made a dark blue icing for one order and have a lot left over, if I add more white to it, will I achieve a "baby blue" color? Customer wants baby blue and pink on her cake...

Most likely it will work.  I would take just a bit - say 1/4 cup ( or less) of the darker blue and see how much white you need to add.  It's hard to give you a real YES! it will work w/o seeing which dark blue was used and how dark it really is.   

Might even try using 1 Tablespoon and count the # of white Tablespoons needed so give you a better idea.  If it takes say 5 or 6 then maybe you could change to using cups (2 1/2 to 3 cups white to 1 blue) to get the amount needed for this new cake.

I do appreciate you taking the time to help me!!! We just had our Easter today, sorry for late reply! I'll see about that on Sunday...

I would start with the white and add the blue. In art class they said always start with the light color and add the dark slowly in small amounts.

Definitely do this. Just mix ti in a tablespoon at a time, too, because once it gets too dark you can't get it back without adding more white.

Thanks Ladies!!!