While solar panels are dark blue, almost black, they are also reflective. This means that they will likely appear white or some other bright color, which may be a big shock (and a big aesthetic problem) if you have a dark roof and the panels are clearly visible.
My parents are NOT amused.
Update: Actually this is only the case when the sky is cloudy, which it was the day my parents had the panels installed. When the sky is clear they look like they do without the reflection.