There are a few things to consider here. First and foremost, Apple includes the Touch Bar as part of the True Tone settings, so if it's enabled, your Touch Bar will become warmer along with your screen (why Apple does this is beyond me, the Touch Bar should be inline with the keyboard backlighting, not the display). So, when your Touch Bar backlight becomes a bit warmer in tone, your keyboard will appear to be bluer by contrast. It's really not, it's just an illusion as it contrasts to the overly warm Touch Bar. When True Tone is turned off, you should see the same backlight temperature (or very close) to the keyboard backlight. Both should look like an even toned white.
Another thing to consider is the default display color profile on Apple's MacBooks out of the box. They always skew really green to my eyes (despite the claimed 'perfect factory calibration', which I've never experienced). I always take down green tones and up blue/reds to make a more desirable profile to my eyes, as I am very sensitive to green. So, if you leave the default color profile as is, your eyes will adapt, but it will make the keyboard backlight look bluer than it really is due to the contrast against the display, which skews green.
Since I always calibrate my displays to show less green, and more red/blue/magenta, the keyboard backlight looks like a normal white light in brighter room settings, but gives the illusion of looking a bit dull in a dark room due to the contrast of my vibrant and blue/red skewing display. So, it's all a matter of what you're used to and what the lighting temperatures of the display, touch bar, and keyboard backlight look in contrast to each other.
Personally, I've always found that the backlight on pretty much all the butterfly keyboards looked a bit too dim and slightly yellow skewing compared to the older 2015 and previous backlights. With variations between units, of course. Whereas the keyboard backlight on the 16" MacBook Pro is way brighter, whiter and more vibrant than the butterfly keyboards (and this comparison is impossible to capture through pictures and videos). And the entire key is lit, so there is no dulling of any characters on the shift, command, and option keys, and so on. Unfortunately, the keyboard backlight does bleed out from underneath the keys on the new scissor switch keyboards, not as clean as the butterfly keyboards due to the extra key travel. But, it's no where as bad as the 2015 and previous backlight keyboard bleed.
