I also have a cremello unicorn  http://beastkeeper.com/pet/260356 that can't be entered.It's because cremello unicorns are chestnut and chestnut it's a red-orange color and it's not counted as yellow.

Was there a recent change in the scoring? I thought I was up around 540k, but I just checked and my score is down to 510970 points. Maybe I'm just misremembering, which is possible, but I really did think my score was higher. But again, I may just be losing my mind here.

Color value depends on the number of pets with this color. When players breed more pets with a certain color, the value of this color decreases. So the scoring in this type of exhibitions is dynamic.