I had galvanic corrosion running tap. Distilled it happens if you leave a loop full of water and don't use it for several months. I had AL and CU blocks with distilled and galvanic corrosion occured on my polarflo TT barbs (light annodizing).
For rad cleaning I recommend prestone radiator flush and removing rad from loop. I have spare mcp300 and run a rad and t line loop. Drain, run a distilled loop, drain, rinse.
Coolant colors
Coolants can be pink/orange like dexcool from GM, red/pink from toyota/waterwetter/ zerex, and purple like Purple Ice from Royal purple which no one recommends.
http://www.royalpurple.com/prodsa/prpice.html
Prestone has blue coolant but i never seen it.