Is this the smallest known rebus puzzle, and what does it mean?
The answer to the puzzle is "Blueprint" but I doubt it's the smallest.
We would need to clarify what is meant by "smallest". If you mean the smallest number of bytes required to store the puzzle electronically, then the answer is no, this is not the smallest puzzle. A4ID (foreign aid) (4 bytes) has less letters and color doesn't matter so there's no need to store the information. R+R (summer) is shorter, still.
Side note: We could get cute with it and say "small print" is the smallest rebus:
I'm not sure whether its the smallest rebus puzzle....but the answer is Blue print!! . . . If by the smallest rebus puzzle you mean the one which has the least number of letters in the answer the NO, there is a smaller rebus puzzle, that being.....Big Deal-
The answer to the puzzle has been given in the other answers, but how about this for a smaller (art-related) Rebus puzzle: