As I recall, sonar often doesn't work very well when the source/receiver is submerged and the target is close to the surface, and this problem gets worse as wave height increases. The problem being interference (scatter) from both the waves themselves and the bubbles they generate. Also, if you stop to think about it, a whale traveling just below the surface might well have a hard time "seeing", a small boat hull (with its sonar) that sticks maybe a meter and a half or two meters under the surface until the whale was pretty close to the target.
As for using their eyesight, remember that a whale eyes are on the sides of its head, and thus can't see anything forward, regardless of the acuity of the eyes themselves. You can see this effect yourself if a whale or dolphin ever comes along side your boat to "check you out", they almost always position themselves parallel to the boat and then roll over a bit to get an eye out of the water so they can see you. So, I doubt that hull color has anything to do with whales accidently ramming boats.
A couple of added thoughts:
Active sonar may well help, IF it is at a frequency the whales can use. There are "noise makers" used on passive fishing gear for just such a reason, to pretty good effect. Also, there is some evidence that Gray Whale migration patterns are altered by coastal boat traffic along the California coast, particularly on busy weekends near busy ports. The thought is that motor noise may be confusing/annoying the whales.
Last edited by SlowButSteady; 10-08-2010 at 08:10 PM.