Pink cup

As part of bed time routine, both Nathan and Evan get given a cup of milk before bed. We have been doing this for many many months now. Lately there's been a couple of times when Evan has decided he doesn't like his milk anymore, and wants Nathan's instead. Even though they are the exact same milk in the same kind of straw cups, only difference is the color of the cup. Because Nathan has claimed pink as his "favorite" color, we usually give Nathan a pink cup, and Evan a different color so we can tell them apart. I guess Evan has noticed this, and decided that he likes pink too. A couple of times we had to negotiate with Nathan to let Evan have the pink cup. Other times I just give both of them pink cups. Evan probably hasn't settled on any favorite color of his own yet, but I wonder if he will end up liking pink because Nathan does?