If I publish a blog in which I concentrate on content and information, I want to make the content and information easy (yet inviting) to read.
This blog, The Real Blogger Status, is marginally easy to read - and looked boring - before I upgraded to a Designer template, which has a more complex background.
If I wanted something stylish, I might have chosen a template with a black background, such as in my Tech World blog. White on black is very elegant looking, yet reasonably easy to read.
Some people like elegant, but mysterious, colours - such as dark blue or red text, on a black background.
Going a step further, some folks will choose black text, on a black background. All three colour schemes are fine for search engine visibility, since search engines don't look at colours - they just look at text content.
Your readers, on the other hand, won't be so lucky. How easily can you read dark blue or red text, on a black background? Worse yet, black on black? You can't. If you're like me, and have seen this nonsense occasionally, and you watch what looks like an otherwise normal blog load, displaying large patches of blank space, you'll get curious.
Look at my "click and drag" demonstration.
How many readers will try click and drag where no text is visible, unless they see a "click and drag here" caption?
Be kind to your readers, if you want readers. Choose text and background colours that complement each other. Elegant isn't always kind.
If you see a blog or web site with an interesting colour combination, use "Red Alt: I Like Your Colors" to check out the colour palette used.