Vim does syntax highlighting by default. If you try to do it on a file that doesn't have a .c or .cpp extension It won't highlight it.
Syntax highlighting isn't perfect, so you might get some weird results every now and then. Doesn't mean you typed something wrong (at least with python it gives no indication). It usually tries to highlight built in commands and such (ex. print, for, while... again, this is in python).
If you wanna turn syntax highlighting off do:
If you want it always off, then turn it off in vimrc. Also you can enable and disable it for specific files.
Take a look at this for reference: