In the old days, coolant was green. End of story.
Then other colours started to arrive, red to distinguish formulations for Asian nameplates, amber colour designated the Dex-Cool formulations, and different vehicle manufacturers further added to the rainbow with their offerings.
Thankfully there has been a rationalization of this.
Most aftermarket supply chains now have a number of universal, or at least near universal, coolants on hand that can be used across many manufacturers, thought not necessarily all.
Green is still there, but has been largely replaced by shades of yellow antifreeze/coolant. Dex-Cool remains in it’s designation amber colour, while there are also red a blue colours for Asian and European applications, though there is quite a bit of variation in approaches so it is best to ask your supplier for a reference chart.
No matter which type or color antifreeze is, it will transfer heat away most efficiently when blended with the proper amount of water – a mixture percentage based on the lowest temperatures typically seen in your climate. Most regions are best suited to a 50/50 water-antifreeze mixture which will provide protection from a low of -34°F to a high of 265°F. In addition, maintaining proper freeze point protection ensures corrosion inhibitors remain at intended levels.
It’s interesting to note that pure antifreeze alone will not perform the task of protecting your vehicle’s cooling system much better than water would by itself. In fact, pure antifreeze will freeze at a temperature not much below where water does. In the coldest climates, the most effective mixture against freeze-up will consist of 60-70% antifreeze (with the rest being water) – not 100%.

Green: This type of traditional antifreeze uses “Inorganic Acid Technology” (IAT) as a chemical basis, and usually contains silicate or phosphate additives to prevent corrosion of metal cooling system components.
Orange and Pink (and sometimes Red): Organic Acid Technology (OAT) Type Coolants Antifreezes died pink or orange have been around since 1996 and feature a newer class of corrosion-preventing inhibitors known as organic acids. They do not contain the silicates or phosphates. Organic Acid Technology (OAT) type coolants were widely used in Europe before being introduced to the North America. They typically have a longer service life of 5 years or 150,000 miles because these inhibitors last longer before breaking down. OAT formulations should never be used on older vehicles that have traditional copper-and-brass radiators, only aluminum or plastic ones.
Variations of this coolant type are used by General Motors in its Dex-Cool along with some European and Asian manufacturers Honda and Toyota have also begun using extended-life OAT coolants. In some cases, it is dyed red. Some European makers use a version dyed pink.

Light Yellow – Hybrid Organic Acid Technology (HOAT). Coolant typically dyed a very light yellow is known as “G-5”. While HOAT coolants typically mix an OAT with a traditional inhibitor such as silicates or phosphates, G05 is a low-silicate, phosphate-free formula blended with a benzoic acid inhibitor.
Combining antifreezes together is of course not recommended.
At best, mixing types of antifreeze will cause the lifespan of the new mixture to degrade to that of the one with the shorter service interval. At worst, different corrosion inhibitors that were never designed to mix will work against each other.
There have been reports that mixing old-school green coolant with an OAT can create a gel, which is flows poorly and can clog passages.

Coolant, while seemingly simple, has become increasingly complex over the years and consequently it is a good idea to refresh your knowledge on a regular basis.