Hello Scott,
So examine say ProPhoto RGB where we have 0R/G255/B0 in LR vs. Photoshop. LR indicates this isn't a 'legal' value where Photoshop just truncates it. I find that useful.
Help me understand this - what do you mean by LR indicates this isn't a legal value? Are we talking about a color that falls *outside* of ProPhoto 0R/G255/B0?
No, we are talking about colors that aren't colors, since they are out of the visible range. Every ProPhoto triplet with 0 for red and green and any amount of blue leads to a L* of 0. So Prophoto blue is a lightless color. Same thing for greens: up from 0/135/0 to 0/255/0 the a* is -128. Values of 136G an above are imaginary colors. For that reason, calculating colors in Prophoto RGB is a nogo in my opinion. MfG Thomas Richard