Red is certainly more rare than green.
I bought a new one in '84 and all the reds were sold out, so I had to get a green one.
I loved that bike! Very good for its day, though the brakes were not good even by '84 standards. Like other KDX since then, the forks were too soft.
Sounds like you do need some clutch work before you ride it.
The '83 and '85 are nearly identical to your '84, except no red plastic was offered. The '86 - '88 motor is very similar except it has a powervalve. I'm not sure if the clutch might also interchange with earlier KDX175s ('80 - '82).