Ultimately it’s about perceptual color versus actual light. A red/blue gradient should be almost entirely transparent (ahem, grey if that’s what you’re getting

Ultimately it’s about perceptual color versus actual light. A red/blue gradient should be almost entirely transparent (ahem, grey if that’s what you’re getting from lack of data in RGB), but it too will “cycle through” and produce colors that don’t exist between red and blue. You’re expressing preference for a particular substitution approach that makes sense to you, which is perfectly fine as a preference but that’s all it is. Edit: or it will produce the full spectrum between red and blue but that’s obviously not your preference.