'Tar' backwards is 'rat'?!! Is this an art term??

The worst kind of grid. Two esoteric categories. What has rat to do with art ? Try these categories : The life of Lawrence of Arabia, German irregular verbs, Anagrams of makes of cricket ball, Battles of the Thirty Years' War. Don't fancy them ? I find them very interesting but I wouldn't make a grid with them.

Easy enough to sort into groups, but a couple of the connections are less "work this out from the clues" and more "read the question setter's mind". And why pink rather than red?