Hey there
If it's not too much to ask, are you able to show photos? I have a piggy bluebelle who is slightly yellowed and she is somewhat similar in color to snuzzle, it sounds concerning that she seems to be brown and it might be from the sun itself, like you mentioned.
I'm leaning towards not sunfading her, it might do more harm than good to be honest.
Could always look on the bright side and pretend she's like a real pony color like Macau Jenny?
(I'm not much help sorry)