As I recall from when I dyed my panels for my SWS I sealed the panels with a thin coat of epoxy.  I never saw any change is color after doing this, since the varnish doesn't come in contact with the dye/stain.   Good luck.

   So this has been glassed so the same is true

https://www.imagevenue.com/ME12880W

   Most varnish does that after those many coats. It has a slight tint which could be a little brownish.  You can use clear automotive finish with RV protection instead of varnish. It comes two part in a rattle can. It is clear but expensive and toxic. 

Personally I get tired of varnishing after three coats. 

   @Grumpy. Any particular brand?

Something like this stuff maybe?

Didn't know such existed until I saw that post of @Grumpy's.

Certainly toxic stuff! So take all necessary precautions to avoid bodily contact or inhalation!

I used this over  a  bright pink aniline stain on blond ceder strips , 8 coats and was and still clear after one year.  It take a lot of coats, very thin finsih and does have UV prtection.

EPF-RCC750 EPIFANES RAPIDCLEAR FINISH 750ML, 6/CS ***PAINT UN1263*** *** No Air Shipments ***

   @ Anthony B. Thanks that may be what I'm after. Since its recommendation is thin coats with no sanding between did you just roll it on or roll and tip?

   I ddi 220 sanding on epxoy and used high quality stiff grey 2 inch brushes  from amazon and the white dense foam rollers from home depot.

I only did the deck ( hull painted white)  8 coats used almost a full quart.

did not sand between coats.  2 coats per day