Move the point to the region of interest and enter C-u C-x =, ie the extended
what-cursor-position that includes all the
describe-char information, which includes the current active face for that character.
position: 52052 of 94583 (55%), column: 3
character: f (displayed as f) (codepoint 102, #o146, #x66)
preferred charset: ascii (ASCII (ISO646 IRV))
code point in charset: 0x66
syntax: w which means: word
category: .:Base, L:Left-to-right (strong), a:ASCII, l:Latin, r:Roman
to input: type "C-x 8 RET HEX-CODEPOINT" or "C-x 8 RET NAME"
buffer code: #x66
file code: #x66 (encoded by coding system prefer-utf-8-unix)
display: by this font (glyph code)
Character code properties: customize what to show
name: LATIN SMALL LETTER F
general-category: Ll (Letter, Lowercase)
decomposition: (102) ('f')
There are text properties here:
Following the link to the face (
font-lock-keyword-face in my example) gives a buffer like this:
Face: font-lock-keyword-face (sample) (customize this face)
Font Lock mode face used to highlight keywords.
Defined in `font-lock.el'.
Which tells where the face was originally defined, and all of it's properties. This method allows discovery and customization of any font face used in Emacs that is accessible using the point, even in the minibuffer.
I'm not certain how to find the equivalent information for faces used in the modeline.