Your gonna get brake down. The UV will react with the propylene glycol and you will get partials appearing in the loop. This in turn will block you water cooling blocks and create a build up if you don't get the right mix. Personally avoid like the plague.

If you going to Do it regardless of what im telling you, you will need to use a Acid based dye so that it will mixed well. If you use a water based dye it will brake up with in days.

Personally it up to you self some time's a cheap alternative will tun out to be expensive repair in the long run.