As you'll have seen from my latest Ponyfic Roundup, I read BillyColt's story This Nearly Was Mine recently. Vinyl Scratch is a major character in this fic, and early in the story she is described as "very pale yellow". Although I didn't note that in the review, it seemed an odd choice to me, and indeed several Fimfiction commenters brought it up, saying she wasn't yellow.
In an idle moment, I poked about a bit online, and on Vinyl's mlp.fandom.com page I found this:
a layout artist on the show noted that the character model's coat color is actually a very pale yellow, specifically the 24-bit hex triplet #FEFDE7.[3]
The citation given is to a locally archived copy of a discussion from way back in April 2011 from the old Allspark forums (slow-loading PDF) featuring a poster called Nayuki who was a layout artist on Friendship is Magic. Another forum member asks Nayuki, "I've heard [Vinyl] was really supposed to be a kind of very pale yellow or off-white. Is that true?" To which the reply is:
Short answer: Yes
Long answer: Yes, she's off-white
Awesome answer: #FEFDE7
Look up #FEFDE7 on various quickly Googleable sites and you get a variety of text interpretations or none at all. These include yellowish white, cosmic latte (I love that one!) and light grayish yellow. I'm not qualified to say which is right, or how approximate those text names may be, so I'll stick with the actual show staffer's description of "off-white".
Still, it does seem Vinyl's coat colour description could be a little less clear-cut than "not yellow in any way, don't be silly", which is what I would have thought earlier.