Sometimes, when you open a document in vim, the color of the font and background is not easy on the eye, like below:
In order to encounter this, you can change the backgroud of vim to use light background, by using
:set bg=lightin vim to become like below:
You can change the backgound back to dark by using
:set bg=darkin vim.
That's all, hope this is going to be useful to you.