It turns out that brake fluid is the only automotive fluid whose color is explicitly regulated, at least on a federal level. A long search through the NHTSA’s standards didn’t turn up any evidence that antifreeze, automatic transmission fluid, oil, windshield washer spray, power steering fluid, or any other kind of liquid is explicitly regulated by color. And a quick trip to O’Reilly or a Google search will reveal that previously mundane fluids are now available in a rainbow of colors. It seems that manufacturer consensus, rather than any specific regulation, is what led to widespread usage of specific colors for fluids such as antifreeze and ATF in the past. The diversification of technology in particular is driving the use of a much wider color palette for these fluids. This bulletin from an industry trade group known as the Filter Manufacturer’s Council outlines the shift away from usage of a single color (bright green) by antifreeze makers. Red, yellow, pink, orange, and blue are some of colors that antifreeze is now available in. And as the bulletin states, no color corresponds to any particular type.