Syntax highlighting depends on two things:
* a tmLanguage file to describe the syntax
* a tmTheme file to color said syntax.
Generally, what you want to do is to identify the scope you want to color (use Ctrl+Shift+Alt+P and look in the status bar or install a plugin like ScopeHunter) and then add some appropriate code in whatever tmTheme you are using like so:
However. I had a quick look and, as is the case with Markdown, the ReStructeredText syntax that comes bundled with Sublime is a little strange (to be polite). For example, the scope "markup.heading.restructuredtext" does not identify the heading (as one would think) but the dashes/equal signs underneath it. You can therefore color the dashes but not the actual text of the heading! Grrr.
That's the gist of it.
You also mention code blocks. Did you mean highlighting the code inside a code block?