As I traverse in the wayback machine to the 1980s, I recall that I originally had trouble with color mismatches when trying to gel my backgrounds. Gelling backgrounds was a popular thing to do, led by Dean Collins' method to easily provide color variety for products and portraits.
Anyway, I used a Larson softbox on my subjects, and aimed another flash head with a standard reflector holding a gel at a black background. The problem happened because the softbox, as any softbox will, warmed the color temperature of the light. But the background light wasn't being warmed. So if I picked a gel that looked good with what the subject was wearing, the background came back looking much cooler. Well, this being the film days, learning the reason why took me a LONG time! Eventually, I found that if I put a slight warming gel over the background strobe AND the color matching gel, everything was hunky dory.
Which brings me to today's lesson (which I apparently forgot). For some time now I've had trouble with my various flash units in my studio. My main 5x7 Larson seems warmer than some of my other lights... a Larson 4x4, two Larson 14x48 striplights for accents, and especially a background light with a 9 inch reflector. I've noticed that my main light seems warm, while the accent and background lights seem cooler. But Larson softboxes are known for their color consistency, right?
Wait a doggone minute Fuzzy! I purchased my various Photogenic monolights separately over a period of years. So I wonder if they all have the same type of strobe tube! You can order them with either a with clear glass tube or a UV corrected glass tube (which is noticeably warmer).
Sure enough... my main light had the UV corrected strobe tube and all the rest were clear strobe tubes! I was wondering why I had to shift my color in raw up to at least 6200 degrees to make it look right, and then the background and accents went blue.
So, I moved the UV-coated tube from the main light to my non-softboxed background light. Now the background looks and accents look right, and my raw conversion color balance is back down where it should be.
Now the only strobe tube that has UV coated glass is the background light... just as I learned (and promptly forgot) 30 years ago. (Picture Fuzzy hitting his head with the palm of his hand... or oiling up his rusty brain)