Summer bib tights

DHB used to do non-thermal lycra tights, but they seem to have dropped them (I guess they didn't sell well enough). But even those could quickly become intolerably warm. I'd go with the P20 (which has an SPF50 version) and shorts

Ride at night?

http://www.wiggle.co.uk/castelli-upf-50-light-leg-skins/

I've got some of these which may be worth a look at. I wear them under 3/4 bib knickers or shorts if I don't want the warmer full winter tights. Obviously can remove them if I get too warm.

Use them for different reasons than you want but reckon they would do the job.

They also do knee & arm warmers in similar material.

I think Wiggle do some DHB Aeron leg/knee warmers that are white and designed to keep off strong sunlight so you could try some of those with your existing bib shorts.

Ultrasun worth looking at too: http://www.ultrasun.com

can't think of anyone specifically making summer tights. X-Bionic do a couple of lighter ones and their stuff is very good at regulating temperature, but they're not specifically designed for tropical heat

https://www.x-bionic.co.uk/men/biking/road-bike/the-trick-biking-pants/5...

Don't think you'll have much luck so.....

Have you tried Riemann P20 sunblock?  It's alcohol based so is soaked into the skin, is sweat and waterproof, once a day application, and, most importantly, works.  I'm a ginger and we arn't known for our lovely tans, I used P20 in Kenya (And Sharm while diving, still worked after being in the sea an hour at a time.) and the only day I burnt was after a morning massage and the oil used stopped the sunblock getting in to the skin.