Also on my other boats I have up to now used International's
Spar varnish, but it has a distinctly yellow colour after application.
Can anyone recomend a colour free varnish that will still give UV
protection.

Traditional varnishes are all amber in color and will get darker as they age. For truly clear finished you need to apply a urethane.

Interlux/International Perfection 2-pot polyurethane is water white (clear). It's more expenive but is more durable than traditional varnish and less coats are required. Epifanes also makes a two part poly varnish (PP Varnish Extra). Another option is Coelan.

If you want to go another route, consider spraying an automotive clear coat. Those urethanes are designed to be crystal clear with high UV protection.