Slight dose of amnesia here. I was doing a lighting test on a mannequin, I wanted color on one side of the face but I got enchanted by the blue, forgot about color balancing.
Are their gels designed strictly for color effect, without temperature change? Sorry I don't have much experience with gels.
Of course there is a color temperature change, which is the point of CTO and CTB gels. I'm just saying that if you want a 3200K key light and your lamp is 3200K, then why do you think you need to add blue gel to it to get 3200K? It's already 3200K!
If anything, the light on the key side is the key plus
the fill, and if your fill is blue, then the light on the key side is a mix of the 3200K key light and the blue fill light, so it probably ends up a bit over 3200K depending on how strong the fill is and whether it is frontal or coming from the opposite side as the key, etc. But it's probably not adding enough blue for you to want to add some CTO to the key to compensate.
Color temp gels have a MIRED shift listing on their color swatch, so you can calculate the shift in color temp. Of course, with a mix of two lights, you'd have to use a color temp meter to know what the final color temp ends up being, but since you were asking if you should put some CTB on the key light to keep it white (i.e. 3200K) if the fill has CTB on it, I'm saying no, if anything it would be the opposite.