docs: use proper quotations instead of '*'

gdk/gdkcolor.c

@@ -132,12 +132,12 @@ G_DEFINE_BOXED_TYPE (GdkColor, gdk_color,
  *
  * The string can either one of a large set of standard names
  * (taken from the X11 `rgb.txt` file), or
- * it can be a hex value in the form '#rgb' '#rrggbb'
- * '#rrrgggbbb' or '#rrrrggggbbbb' where 'r', 'g' and
- * 'b' are hex digits of the red, green, and blue components
+ * it can be a hex value in the form “#rgb” “#rrggbb”
+ * “#rrrgggbbb” or “#rrrrggggbbbb” where “r”, “g” and
+ * “b” are hex digits of the red, green, and blue components
  * of the color, respectively. (White in the four forms is
- * '#fff', '#ffffff', '#fffffffff' and
- * '#ffffffffffff').
+ * “#fff”, “#ffffff”, “#fffffffff” and
+ * “#ffffffffffff”).
  *
  * Return value: %TRUE if the parsing succeeded
  */