Ever wonder where a certain word (saying) comes from? Click here for a great site - this is just one of the explanations for SMART AS PAINT:
[Q] From Lewis Rosenbaum: “The phrase smart as paint is said by Long John Silver to Jim Hawkins in Treasure Island. Any ideas as to the source of the expression?”
[A] It appears a couple of times in R L Stevenson’s book, the first time as: “Now, Hawkins, you do me justice with the cap’n. You’re a lad, you are, but you’re as smart as paint. I see that when you first come in.”
It was only one of many versions that have been invented from the 1850s onwards, among them fresh as paint, snug as paint, clever as paint, pretty as paint, and handsome as paint. They’re all similes that draw on some special quality of paint, but smart as paint punningly combines two senses of smart — the idea of new paint being bright and fresh in appearance and that of a person who is quick-witted and intelligent.
It seems to have been Stevenson’s own invention. At least, I can’t find an earlier example. It started to be used by others in the second decade of the twentieth century, presumably based on its appearance in Treasure Island.
But it wasn’t always a pun; sometimes only the first part of the sense was meant. For example, this appears in Sir Arthur Conan Doyle’s A Visit to Three Fronts, dated 1916: “His charming blue uniform, his facings, his brown gaiters, boots and belts are always just as smart as paint.”