My recollection is that Holley Red pumps came out first, and they would stop pumping after they got hot, due to the internals getting longer and not having enough clearance built in to be able to compensate. Holley started warrantying them with other color pumps so they could tell by looking at the color to see which ones were working when out in the field. I also recall they had some black ones too. There may also have been some other color coded ones that I didn't see. Blue ones started coming out in late 73 as I recall.