Pressure plate spring colors
 

I have a couple of pressure plates and discs. I've been trying to figure out where they belong. So, I started with the "Green Book". They list several pressure plates in various diameters, but with a variety of spring colors listed. For example: 51 7563-A for 39-47 4-spd commercial with gray colored springs and 81B 7563-A same size (11") for the same application with black colored springs. Also blue, orange and green springs are listed for other sizes and apps. Can anyone shed light on this mystery and tell me what colors go where and what they mean?

Re: Pressure plate spring colors
 

from 1947 trans,clitch,pto overhaul publication # 3697-47 page 78
11" clutch --115-120 lbs, grey
10" clutch 125-135 blue
9" clutch 147-153 brown spring pressure at 1-9/16"