Your question should be more accurate. You can compose a function to do what you want. For instance to highlight saturday and monday using the color pink (you can have a try in interactive mode ):
(defun my-highlight-we-agenda ()
" your function description "
(highlight-regexp "saturday\\|sunday" 'hi-pink))
Next you active this function ...
Even you are using global-hl-line-mode. You have to still be sure local variables(Which can be different for different buffers) are correct.
I have like that definition in my files. Reverse should be correct for you.
;; Don' use globl-hl-line-in-org-agenda
(add-hook 'org-agenda-mode-hook (lambda () (setq-local global-hl-line-mode nil)))
I highly ...
highlight-chars is nice and general, but whitespace-mode is better for the common case where you mostly just care about tabs and spaces. You can configure it to change the background color of inappropriate whitespace characters so that they become obvious, or you can use it to show a glyph in their place, or both.
The one annoyance that I've had with ...
You can use library highlight-chars.el to highlight any characters you like.
See commands hc-highlight-chars and hc-toggle-highlight-other-chars. You can specify characters in any of these ways:
using character classes (e.g. [:digit:])
using character sets (e.g. iso-8859-1' or lao').