Face color changes

[Juri Linkov]

I noticed that some face colors are bad choices.  The worst example
is "RosyBrown" used for font-lock-string-face on light backgrounds.
It has high intensity which corresponds to light colors.  No wonder
that this color is hardly visible on light backgrounds.

I got the formula from x_alloc_nearest_color_1 to calculate a dark color
nearest to "rosybrown".  The code is below:

(let* ((frame (selected-frame))
       (color-values (mapcar (lambda (v) (lsh v -8))
                             (x-color-values "rosybrown" frame)))
       (c-r (nth 0 color-values))
       (c-g (nth 1 color-values))
       (c-b (nth 2 color-values)))
  (list-colors-display
   (delq nil (mapcar
              (lambda (c) (and (eq (color-mode (cadr c)) 'dark) (cadr c)))
              (sort (mapcar
                     (lambda (c)
                       (let* ((c-values (mapcar
                                         (lambda (v) (lsh v -8))
                                         (x-color-values (car c) frame)))
                              (d-r (- c-r (nth 0 c-values)))
                              (d-g (- c-g (nth 1 c-values)))
                              (d-b (- c-b (nth 2 c-values))))
                         (list (+ (* d-r d-r) (* d-g d-g) (* d-b d-b)) (car 
c))))
                     (list-colors-duplicates))
                    (lambda (a b) (< (car a) (car b))))))
   "*Colors-Nearest*"))

(defun color-mode (bg-color)
  (let ((frame (selected-frame)))
    (if (let ((bg-color-values (x-color-values bg-color frame))
              (white-values (x-color-values "white" frame)))
          (>= (+ (* (nth 0 bg-color-values) 0.30)
                 (* (nth 1 bg-color-values) 0.59)
                 (* (nth 2 bg-color-values) 0.11))
              (* (+ (* (nth 0 white-values) 0.30)
                    (* (nth 1 white-values) 0.59)
                    (* (nth 2 white-values) 0.11))
                 .5)))
        'light 'dark)))

It suggests to replace "rosybrown" by "plum4" or "PaleVioletRed4", and
"orchid" (for font-lock-builtin-face) by "MediumOrchid3" or "DarkOrchid3".

If this is correct, other face colors could be improved as well
to match their background mode (i.e. to use light colors on dark
backgrounds, and dark colors on light backgrounds).

-- 
Juri Linkov
http://www.jurta.org/emacs/