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.
They also do have some regional variations, populations who've adapted to their environments compared to their desert cousins.
The Shattered continent baleens are isolated from their Horseshoe continent cousins. Over time, their more volcanic environment has driven them to develop more tough skin and darker colors.
Tundra Baleen have adapted by bulking up and getting more "fuzz" on their body. They've mostly abandoned fishing with their arms and use specialized nets to catch the shrimps and other small marine life they subsist upon.
Finally, the mangrove baleens have a taller, more lanky subset who live in the hotter parts of the region. They tend to spend most of their time wading through the shallows of the mangroves, and their longer legs help keep their bodies away from dangerous roots and critters.