Just like the page you are currently viewing.
If in doubt, you may find that choosing a plain white background is the best idea. You can always use texures, or other background designs on small areas of the site. A plain background is simple, clean and can look modern and professional.
All Over Pale Colour
All over background of a very pale tint of one of the colours in your chosen colour scheme.
White and a Colour
Using one of the colours in your chosen colour scheme, or a lighter or darker version of it.
A Colour Gradient
Seamless Background that You Provide
Make sure that you buy a file in png or jpg format, rather than a Photoshop or Illustrator pattern, unless you own the software and know how to work with patterns.
Here are some examples to give you some ideas.
“Subtle Grey” from subtlepatterns.com (this is a website with lots of different backgrounds that you can download for free.)
A striped background made using stripegenerator.com.
A seamless brick effect background from Pixeden. This kind of background should be used with care, as it’s not an approach that will work for every site.
A large background photo, like this one by valiunic at Pixabay can be effective, but again it won’t work for every type of website and you need to be careful with the size of the image, so as not to slow down the loading time of the site too much.
Paper Effect Background
See the examples listed for the Doodled Style. These backgrounds could work with any of the other styles too.