I said some time ago, somewhere, to someone (I think @Luther) that MLV App's tint slider is not very good because it is done in final colour gamut - I was mistaken. It is actually done at the very start, on camera RGB channels. So it is fine, rawtherapee even does all white balance that way, so doing a little part is not harmful. Also I did spend about an hour messing with the white balance function, so this could change soon.
As for the icon. I am thinking, soon will have an answer,.