The Hellfire designer thought about the fact that colored springs on your car can sometimes just simply look disco and the race savvy competition can see what spring rates you are running from a hundred feet away. While stealth black is always the cool color to use, the Hellfire springs do have color markings at the top of the springs to indicate six different spring rates to choose from. This offers a wide range of tuning of the suspension to improve the handling of the Hellfire on a variety of different surfaces. The factory Hellfire spring settings are Silver for the front and Yellow for the rear. The Hellfire spring ends are precision ground for a flat surface on the spring perches. To help aid in tuning, each spring is rated in gf/mm and comes with a handy spring chart. (sold in pairs) $7.00
 
#86549 SHOCK SPRING 18x80x1.5mm 12.5 COILS (BLUE 71gF/mm)
#86550 SHOCK SPRING 18x80x1.5mm 10.5 COILS (SILV 89gF/mm) (kit part)
#86551 SHOCK SPRING 18x80x1.8mm 14.5 COILS (PINK 134gF/mm)
#86553 SHOCK SPRING 18x80x1.8mm 12.5 COILS (WHIT 159gF/mm)
#86554 SHOCK SPRING 18x80x1.8mm 11.5 COILS (YEL 177gF/mm) (kit part)
#86555 SHOCK SPRING 18x80x1.8mm 10.5 COILS (RED 196gF/mm)

http://www.hpiracing.com/pdf/hellfire_springchart.pdf