The colouring scheme matches the colours typical of Edison plug fuses;
Blue=15A
Red=20A
Green=30A
Grey=40A
Above that black handles are used.
If you have found a 40A Edison plug fuse, I want it for my collection.
Blue, red, and green are correct, and several breaker manufacturers have used these colors for their handles. I'm remembering Bryant before their breaker business was bought by Cutler-Hammer.