Question

A point source emits light of only a single frequency = 6.7 x 1014 Hz. What color is the light produced?

Answer 1

$$\lambda=\frac{v}{f}=\frac{3\cdot10^{8}}{6.7\cdot10^{14}}=448\cdot10^{-9}\ m=448\ nm$$

Indigo color is produced.