Different color spectrum. They also morph depending on where they are in the tank. I got 2 nems recently from a local reefer. She had 50+ all clones of the same mother. Some were red, some pink, orange, rainbow, etc. they are ALL E. quadricolor. You can play around with the spectrum a bit if you want, but chances are, you're looking at your happy new pink nem.
Just make sure it's turning pink and not bleaching out. If you start to see it going transparent then you need more light.