My question is how to customize this kind of blocks' background color?
You don't say what "this kind of block" means, or how your "blocks" were caused/created.
Anyway, it sounds like you are asking how to know which face is used for that text with the yellow background, so you can use
M-x customize-face to change its appearance.
The answer to that is to put the cursor somewhere on that highlighted text and use
C-u C-x =. The
*Help* output will tell what faces are used at that position, for both text property
face and overlay property