A metallic surface ejects electrons when exposed to green light of intensity I but no photoelectrons are emitted when exposed to yellow light of intensity I. It is possible to eject electrons from the same surface by 

The VIBGYOR pattern, representing the colours of visible spectrum in increasing magnitude of wavelength, shows that V-I-B-G all have $\lambda$ less than that of yellow colour and hence can initiate photoelectric effect irrespective of intensity.