Many people design the look of their sites on a whim. They dont follow rules and this is good news for their personal growth, creativity and sense of well being. However it does very little to make them rich.
If you want to get rich from building websites you should follow a few rules about how a website actually looks:
There are thousands of newspapers in the world and ALL OF THEM use dark text on white paper. This is not because of a lack of design expertese. It is because it is easy to read. Your website should be easy to read too.
Have you ever stared at small red text on a blue background? It can actually give you a headache. If you want to be rich, dont do it.
About 5% of the population of the planet are colour blind to some degree. Why would you want to drop your income by 5%. Make it easy to read.
Same thing goes for dark text on a dark background.
If you want to reverse out (light text on a dark background) use it for BIG headlines only.
Try to keep your pages looking simple and calm. Dump any small spinning gifs and jumping whatnots. Animations can look really unprofessional and should be used sparingly.
Ok, now here is the really hard bit.
Follow these rules, but do not forget to make your website look good. ...Ouch,
that is the difficult bit. This is why we have designers in this world. If
you cannot afford a designer, look around at some big professional websites
and see what they do with colours. You will see they stick to the rules yet
still manage to create exciting, vibrant sites.