There are yellow leathers, just not "lemon" yellow that you might be expecting. I found some images to help explain:
Bleached out yellow leather, what you'd see in a store
Transitioning to normal color, but looks really nice and bright yellow
Natural color that you should expect in the end, right on the mariculture racks in the ocean
There will be slightly nicer ones, and blue leds or actinic bulbs MAY help the yellow pop a bit, but they should all end up about the same