So the Baleens do come in a variety of colors, influenced by diet and environment. Age can impact their coloration as well (infants and kids tend to be creams and yellows) and as they age, their colors to tend to fade and grey out.

These aren't hard rules when it comes to colors and markings, but more guidelines for myself. There could be more blues, more yellows, etc. As long as it's somewhere in the yellow-green-blue range for the most part.