To be honest, I have stared at those two diagrams a lot, both last night, and again this morning, and the only difference I can see is that the “B” does not have an arrow next to it in the second image. What am I missing?
Sorry, I didn't mean to keep you up all night
The arrows are meant to show the change in one particular colour as it is converted. With RC, a colour outside the gamut moves to the edge of the gamut (de-saturated in effect) and a colour in gamut stays the same. With Perceptual, all colours change, compressed into the gamut, rather like compressing a soft ball into a smaller size.
I hope that has not confused you more. If it has, I hope someone else (like expert Mike maybe) can explain it more clearly.
I've been slowly learning about CM over the last 4 or 5 years, it's a long learning curve
Terry.