Hellp, I hava a similar problem with the WB, when I want to customize it. On single files, I can just use the slider, but for automatization I would recommend to implement the idea of setting WB by a formula, what is amore general approach and will include the functionality of your proposed fine tuning slider too. There is camera WB info (guesstimation), there is RT auto (guesstimation), there is apersonal preference cooler or hotter, and there is the wish of guys like me to preserve a little of the WB "look", e.g. no full compensation but keep tungsten indoor fotos slightly warmer and cloudy outdoor fotos colder (but not too much). Also, two independent guessing algorythms tend deviate less from the "real value" in most cases, if averaging over both is done. So why not implement the possibility to enter a formula based on the variables WB cam and WB auto, like in my case,
for example. Another user who likes auto WB but a little warmer, might enter:
Just an idea. Also that green <-> magenta guessing could improve typically if one could do an average of what the camera thinks and what RT thinks.
To give everybody the ultimate hit in confusion, I just need to add that what we call cool is very hot and what we call hot is cooler. 5700K sun surface is way hotter than "just" 2900K glowing tungsten surface in a light bulb. Please everybody think about that and consider using hot and cold in the right way.