WordPress' built-in editor has an HTML mode that lets you override the background color of a post by changing its CSS (Cascading Style Sheet) background-color attribute to the color of your choice.

Your Tumblr theme sets the background color of each of your posts. Tumblr also offers you the option to edit your theme to further customize your design. For example, you can change your posts ...

But you don’t need to use it, and your sites can still look good without it. How Do CSS and HTML Work Together? If you learned about the web a long time ago, or taught yourself the basics, you may be ...