Are the "hub caps" you mention actually the flanges of the axles where they bolt to the hub? This is the bolt pattern that inside of and smaller than the bolt pattern of the wheel itself.

I see no reason for them to be green.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-