D3's suggestion of letting the earth regulate the temp swings is probably the best bet if you are concerned about temperature control, but you can also look at making a jacket for your buckets (I'm assuming you're thinking 5 gal buckets for DWC) out of thermal bubble foil (or whatever it's called) if you can't bury your buckets. Burying your buckets will create a whole new issue with draining/water changes and movement of plants in general.
Boutros used to wrap his buckets with foil tape used in AC duct work back when he was living in Cali and active on this site.
If you have an HOA and neighbors who like to complain about anything that isn't "normal" (which is what I have at my place), a couple coats of white spray paint will at least reflect some of the solar radiation that a black bucket would otherwise absorb, and hopefully won't set off the neighbors. Check Pinoy83's glog. He's in Hawaii doing a Kratky Lowes bucket in what looks like full sun, and the last I saw that pepper plant didn't look like it was struggling.