here's something that might help, . My thinking is that its important as the fact that it quick responds to very low amounts of light, also if you think of the colour spectrum, violet light is the highest frequency we can see so being sensitive to blue might mean its sensitive to the weakest light .. what do you think ?
Also remember, the ability to see colour is not as important as seeing at all in minimal light, natural will use whatever is available to adapt an animals to its environment.
Rhodopsin works not because they detect colour but because when light hits the rhodopsin it causes a chemical change which causes it to decompose. This decomposition changes the rhodopsin molecule to active rhodopsin and the active rhodopsin changes the charge of the rod cell. This creates an electric current along the cell which is sent to the ganglion which is connected to the optic nerve. The more light the more electric current. The optic nerve will then send the message to the visual cortex of the brain where the light will be interpreted as an image.