I am a plumber, and I have a different theory to this one.

"Vivid blue color" does NOT sound like purple primer to me. The primer is very thin and as such tends to be a more faded, dull color, either purple or bluish. What IS a "vivid blue," however, is Rain or Shine PVC cement. It's intended for PVC only, and can set even in damp or moist conditions (hence the name). You'll see a lot of jacuzzi or whirlpool tubs with it around the connections -- it's a very pretty, deep color of blue. Also, CPVC cement is typically yellow for the regular stuff, or orange for the all-weather variation which has a colder temperature range. (Similar to the light-green lable and dark-breen label PVC cement cans.) As such, even when the primer is applied to CPVC beneath the CPVC cement, most of what you see around the pipes will be the yellow or orange color, not a vivid blue.

So if it is the Rain or Shine PVC cement, then it's not formulated for CPVC. Exactly what difference this makes I can't be sure. I've seen CPVC cement ran on PVC drain lines without a problem, and even ABS on PVC DWV lines without issue. BUT -- since this is CPVC and meant as water distribution, I'd hate to have a water hammer blow apart a connection because the solvent weld didn't take.