Aesthetics does matter, but it's not the most important point. I'm more likely to buy a vibe if I like all aspects of it, though, so if the colour is bland or undesirable, I'm probably going to keep shopping unless it has some really awesome selling point.
The colour of a toy is definitely important! No one is going to want to use one that is a bland or undesirable colour! The point of a toy is to have something pleasing, both to the body and the eye, and it is sometimes hard to find a toy that functions well and comes in a good colour.
When there's an interesting colour option available for a toy I actually tend to go for the uncommon colors as my collection has so much black and purple with it, I'm excited to find toys in orange or green or something a litte different from the norm
Ultimately I don't really care what it looks like - chances are I'm not going to be staring at it during use anyway. But initially, I notice that things that are closer to flesh tones or pinks attract my attention. For everything else in my life, I love having bright green or blue or yellow, but something about having a green or blue or yellow vibrator just seems strange to me. And translucent ones where you can see the internal parts or sparkly ones just reminds me that it's a robotic toy and that weirds me out for some reason...