If grit was a colour it would be pink. Fact.
There's no special name for green when you mix some white in. Well, there is - it's called Paradise Green according to Dulux, but I bet you didn't know that. If you're not going to get technical, then green is always green, no matter how much white you put in. All the colours are like that, except for red, which suddenly becomes pink with the addition of some white.
It's called an anomaly.
Someone, somewhere, obviously thought that 'pale red' wasn't sufficient a monicker, and came up with the word pink. I don't know who that person was, but I do know who first used the term Millstone Grit: it was John Whitehurst, and he wasn't a rock tapper by trade but a mechanical engineer from Cheshire. Like pink, gritstone is something of an oddity, just a shade of sandstone with a special name. Lots of sandstones have their own names, just like Paradise Green, but none of them are quite as ingrained in our language as the ubiquitous 'grit'. It's a climber thing really - the sticky, abrasive brown stuff seems to deserve it's own name, it's definitely worth it.
Red, the much celebrated colour of danger hasn't suffered from pink's separatist tendencies. Probably because it makes you go faster. Poor old sandstone, mother rocktype of the much celebrated gritstone gets a pretty hard time in Britain, unjustifiably so. Frequently dismissed as soft, crumbly rubbish, many climbers forget that there is more to sandstone to the soft, crumbly rubbish down South (I jest...). If you visit the excellent sandstone of Northumberland you'll find something not too dissimilar to grit, to mention nothing of the brilliant sandstone around the world. So next time you're bearing down on some boulder problem at Stanage, or climbing splitters at Millstone, just remember it's all just sandstone. More love for the sand.
Torridonian sandstone is maroon, in case you were wondering.