Speedometer pinion colour

[pingis]

Today I am cleaning a gearbox so I can replace the old one which is very hard to shift from second and fourth gears to neutral. While cleaning the "new" gearbox I noticed the nut that holds the speedometer pinion is bright red as a London double decker. Are these nuts colour coded showing what end gear ratio they fit? Our 1957 Moggy has a kmh speedometer. The donor car is slightly younger but also had the 948 engine and a "smooth case".