Pink + Green = ...Blue?

I put my Pistachio NYX Macaron Lippie on my top lip and the Rose Lippie on my bottom lip to take a cool Valentine picture with a Sweetheart, and after I was done, I rubbed my lips together to see what kind of a color it would make and it turned....blue? It was a super cute baby blue! Why on Earth did pink and green make blue? No idea!