Enumerate all of the legal clues that Alice can give.
Of these possibilities, what clue should Alice give?
Alice can clue blue to Bob as a Play Clue on the blue 2.
If she did that, Bob would write a card note of "blue 2".
Alice can clue number 2 to Bob as a Play Clue on the blue 2.
If she did that, Bob would write a card note of "yellow 2, blue 2, purple 2".
By default, Alice knows that color clues should be preferred over number clues. Specifically, in this situation, Alice knows that a blue clue will communicate the exact identity of the card, while a number clue would communicate three different possibilities.