I have a Q about color temps WRT lighting. I have a Coralife Actinic
bulb that came with the (used) hood I bought a couple years ago. It's
labeled as 7100K (FR40-T12-360-BP), and it is *BLUE* when it is on. I
still have this bulb, but I don't use it any more because it was almost
like having a blacklite in the tank - very intense blue cast. Is a
10000K bulb going to be even 'bluer' than the actinic, or is the actinic
a special kind of bulb that is just super blue in color?

The actinic is a special bulb. In fact, it's impossible to assign it a
Kelvin rating, because it's so monochromatic. They pulled the 7100K
number out of... well, you get the idea. It's actually pretty common for
K ratings to be anywhere from slightly fudged to completely bogus.

I did some searches for info about what 'actinic' is, and it almost
seems like it *is* a sort of blacklite or UV bulb meant to enhance the
colors of corals and other critters found in reef tanks.

Yep. Actinics produce light just below (and sometimes slightly into)
the UV range.

steve