Flash is a great idea, but keep in mind your marketing strategy. Flash at the present time is not too search engine friendly. The menu is a cool idea, definitely, just keep in mind the customer. Imagine an old lady on your website chasing the menu around - I don't think she would like that.
As far as the colors are concerned, pick a color any color, just make sure the layout is clean and well complimented with supporting colors and allows ease of reading.
Just so you have an idea of a black website that I've done. Visit the
Dataracks Evo Concept for a rough idea of what I'm talking about. I'm not saying your idea is bad, it's good. Just keep in mind your customer. At the end of the day even if your website is good or bad - all that matters is the relationship you fostered with the client and how you made the client feel after the work was done. You don't have to be a seasoned web developer to run a computer repair company, of course it would help.