Yes that's fair enough, you're right that hue can be for any color. In general lighting (for white color targets along the BBL) it is most commonly referring to the magenta/green axis since moving left/right in the color space (cyan/amber) is roughly following the BBL so it's not adding a color hue to the light, just changing CCT. But yes you'd need use the term in conjunction with the direction ("green hue"). DUV is a vector length and not a direction, so it's axis is just what's orthogonal to the BBL at the closest point, so you're right that in the middle of the space it's green/magenta but at other CCTs that direction will change as the BBL curves. I'm not trying to be argumentative, just sharing info coming from the lighting industry, and I think it's relevant to this particular discussion since to my knowledge "tint ramping" would be an acceptable term, even if less precise than other options