Define "executable file" and a file's "mode".
If you mean something that ls recognizes as executable and flags as such, with an asterisk (*), when you use ls switch F, then Dired+ highlights that. It uses face `` for the asterisk.
;; For this to show up, you need `F' among the options in `dired-listing-switches'.
;; For example, I use "-alF" for `dired-...