If a cluster of stars is all the same color, what could that mean?

Cluster HR Diagrams: Since all the stars in a cluster formed at the same time, they are all the same age. A very young cluster will have a HR diagram with a cluster of T-Tauri stars evolving towards the main sequence. ... Each star is plotted by its color and magnitude on the HR diagram.

the correct answer is a

answerleaving cheese out to get moldy;