There are so many different antifreezes and antifreeze colors these days that you can't really identify just by color. I run roughly 30-50% (don't bother to measure carefully) of Prestone Extended Life "Any Color" antifreeze, mixed with RO purified drinking water from the kitchen.
Buying the "50/50" stuff from the store seems like a waste of money to me. Even though the price per gallon is less, you have to use twice as much to get the same concentration. So in effect, you are paying around $10/gallon for water. More than I'm willing to pay for convenience.
I don't have the link handy, but I've seen a rather lengthy article on why "Dexcool" is probably not good to use in classic cars. Basically, it's additive package is not compatible with other types of antifreeze, and the additives stick to the walls of the cooling system so it takes a complete chemical flush (or all new components including the engine block) to safely switch. The Prestone "Any color" supposedly has a hybrid additive package that overcomes this problem.
I'm not a believer of the "use hard water" theory. While it's true that minerals can coat and protect cast iron in some cases, they don't do anything for dissimilar metal corrosion, which is the big problem area in a TR. That's what the additives in the antifreeze are for. And those same minerals make lousy heat conductors as well as creating pockets that can form steam bubbles. Ask any boilermaker if you should use hard water in a boiler ...