Welcome Tony!
I guess you're gardening in Southern California? Maybe the pot color / soil temperature matters where you live, but up near the Canadian border, not so much! I make my beds out of concrete paving stones stood on edge, and I never thought about the color.
During a dry spell, I can tell that they dry out rapidly at the corners and edges because the concrete is porous and wicks water. For water conservation, I line them with heavy plastic saved from bags of compost and mulch.
I'm going to go out on a limb and say
"probably don't worry" about galvanized steel in contact with vegetable root zones. Sure, acid rain and just plain water and soil will leach some Zinc off the galvanized surface. And the plants may (?) take up more than they need of it (but I don't know that for sure).
The good news is that Zinc has very low toxicity, and sometimes 100-300 mg per day are
prescribed for some medical conditions. But that much might interfere with copper uptake (in you, not the plants). 15 mg per day is necessary to humans.
http://en.wikipedia.org/wiki/Z...
http://ajcn.nutrition.org/cont...
Can you even GET 100 mg (1/10th gram) off a large galvanized container if you sandblasted it and extracted it with acid to get every atom at one time, and then drank it down in one dose? MAYBE ...
... but even so you would have to do that every day for weeks to reach the point where it would affect you noticeably.
And I am very sure that you can't get that much from your raised bed on a daily basis!
However, many people are very concerned about what they put in their bodies, and hopefully someone will give another perspective.
