Im pretty certain Onvi Yellow IS lacquered, and unfortunately it may well get a whole lot worse than mere fading
My 01 Onvi Yellow
Cupra has faded badly, and around a year ago the bonnet / roof (which were most faded) started to peel in little patches. There was still yellow paint underneath, it was just an opaque white crispy layer that was peeling off.
Here's a link to a pic of what mine started doing a few months ago (too big to embed)
Piccie here
Anyway, its got worse since then and seemingly spreading like a skin disease that would only be rectified with a respray, so when I washed it last week (for the first time in a while), I thought I'd put the hose on the flaked bits and see what happened.
This is the result...
Youtube video
If that's not lacquer then what it is?!
Bear in mind this was just a normal garden hose, not a pressure washer! This is the end result...
Pic1
Pic2
Pic3
Im now left with a completely "peeled" bonnet apart from a few bits around the front grill which obviously dont get so much sunlight so havent faded/rotted as badly. Ive also since completely peeled the roof and most of the rear boot lid. Whats left is a very dull matt finished paint, but at least its one that is all one colour and doesn't look like its had acid thrown all over it.
Ive used some T Cut on it and it does come up to a shine, but not quite as good as the original lacquered, so I might speak to a bodyshop to see if I can get it buffed and then possibly re-lacquered.
I wouldnt recommend going this route unless your car gets as bad as mine did, but for me its actually a lot better now than it was, and I might even get away without a full respray that I thought was inevitable. Its also worth pointing out that all this has occured on a car Ive known from brand new as I bought it off a good friend who had it from new, so I know it hasnt been resprayed (unless done before it was sold "new").
Chris