About 40,000 miles down the road the coolant light would have come on. This is VW saying "it's time to change the coolant." You would then have discovered that magic VW coolant is only available from VW and Audi dealers, who will charge you $70 a gallon. Also, their parts department isn't open on weekends. Also, if you mix garden-variety prestone with $70-gallon magic VW coolant, the shit will turn into gelatin. Inside your engine. Because VW hates you.
It is most assuredly not like that with all cars. Green and yellow - fine Green and blue - fine Yellow and blue - fine Blue and orange - death Yellow and orange - death Green and orange - death Orange and orange, if one of them is VW - death VW uses "Hybrid Organic Acid Techology" (HOAT) coolant, which is available from VW and VW only.