I didn't do this cake. Does anyone know what the blue color is? TIA

I think it looks like sky blue (what colour you end up with will of course depend on how much colour you add).

edited to add:
Here's americolor's chart:
http://www.americolorcorp.com/colorchart.html

I used Wilton Sky Blue for my last cake- http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1350625

It looks pretty close to what you are going for.