I had the 'breed a premium pearl (ee Prlprl CcrC)' quest and the quest was solved with a Buckskin. Historically, it was always palomino pearl that solved this quest. If the quest has been updated to only need Prlprl and CcrC, could the quest wording be corrected?

That looks like a buckskin pearl, not a plain buckskin which would have a black mane and tail. A buckskin pearl would have CcrC and Prlprl, the genes important to the quest, regardless of other color modifiers.

Buckskins are Ee or EE, not ee. In this case, the horse is Ee since I was using an apricot stallion. Based on the genetics given by the quest, (ee Prlprl CcrC), only a palomino pearl (ee/Prlpr/CcrC) should solve the quest. I've done this quest many times over the years, and this is the first time that a black based horse solved the quest.

Oh I missed the ee in the brackets. I've also completed this quest many times in the past and I've never noticed it needing a specific base color to complete, so I think it's just a typo, though it would be great if Eve could fix that to prevent further confusion.