Does anybody have a definitive answer on what the color of the vent caps signifies?

A popular vendor of reproduction "show quality" batteries tells me that the color of the vent caps corresponds to the size of the battery.  Green=group 24, red = group 27....etc.

Other people that would remember (because they were there..) tell me red caps are more associated with the 50s, and green caps with the 60s.

What it boils down to is that our car (1956) has a group 24 battery with green caps as shipped from the vendor, but nearly everybody we meet at shows have switched their comparable battery to red caps.  Obviously a point of anal-retentiveness, but some of us are OCD and proud of it....

Good question! I went with red, but depending on what you find out, I may need to get a green tar topper!

http://www.forwardlook.net/forums/forums/thread-view.asp?tid=35938&posts=16&highlight=battery&highlightmode=1#M270886

As far as tar toppers go, you can also get blue, yellow, and I think white.  On their site, they say yellow is GM / AC Delco. 

I wonder if the colors just depended on who the suppliers were?  When I was making my choice, it seemed there were varying opinions.

I think I had heard that "red = '50s" too, and I went with it.