Our brain can easily adjust to different lighting conditions, yes. If we’re exposed to predominantly one color temperature and tint, it’ll generally look white. White balance is the camera’s way of dealing with the same situation; you can white balance to make just about anything look white.
Unfortunately, that’s not all there is to it. You have to remember that those photos are being viewed by people with different monitor calibrations, sitting in rooms lit differently. Nothing you can possibly do is going to make a beamshot accurately represent the true color of the beam to everyone who views it.
The easiest way to deal with this is to treat beamshots as a comparative tool, not an absolute reference. Use manual white balance, and indicate what setting you used (ideally always the same setting), and people will be able to understand more clearly how various light sources compare. You could make an argument for 6500K, since most monitors are backlit with something in that ballpark and you’ll probably end up with the most accurate absolute representation, but I personally use 5700K because I think it’s a more sunlight-like reference and gives me a better relative representation for how I’ll feel about each light.
Ultimately, the most important thing is just picking a consistent reference point and sticking with it. You can misuse white balance to make any source look good or awful, so it’s best to not let it. Use presets or manual and the problem disappears.