\version "2.19.23"

#(define (key-signature::special-print alt-color-list)
   (lambda (grob)
     (let* ((inter (/ (ly:staff-symbol-staff-space grob) 2.0))
            (mol empty-stencil)
            (c0s (ly:grob-property grob 'c0-position))
            (is-cancellation? (grob::has-interface grob 'key-cancellation-interface))
            (padding-pairs (ly:grob-property grob 'padding-pairs))
            (fm (ly:grob-default-font grob))
            (alist (ly:grob-property grob 'glyph-name-alist)))
       (let loop ((s (ly:grob-property grob 'alteration-alist))
                  (stil mol)
                  (last-glyph-name #f))
         (if (pair? s)
             (let* ((alt (if is-cancellation? 0 (cdar s)))
                    (glyph-name (ly:assoc-get alt alist))
                    (acc (ly:font-get-glyph fm glyph-name))
                    (pos-list
                     (key-signature-interface::alteration-positions (car s) c0s grob))
                    (p (car pos-list))
                    (color (assoc-get p alt-color-list))
                    (acc
                     (if (color? color)
                         (stencil-with-color acc color)
                         acc))
                    (padding (ly:grob-property grob 'padding 0.0))
                    (handle (assoc (cons glyph-name last-glyph-name) padding-pairs))
                    (padding
                     (cond
                      ((pair? handle) (cdr handle))
                      ((and
                        (string=? glyph-name "accidentals.natural")
                        ; ...
                        )
                       (+ padding 0.3))
                      (else padding))))
         
               (loop (cdr s)
                 (ly:stencil-combine-at-edge
                  stil
                  X
                  LEFT
                  (ly:stencil-translate-axis acc (* p inter) Y)
                  padding)
                 glyph-name))
             (ly:stencil-aligned-to stil X LEFT))))))


{
  \override Staff.KeySignature.stencil =
  #(key-signature::special-print `((4 . ,green) (-3 . ,red) (1 . ,blue)))
  
  \override Staff.KeyCancellation.stencil =
  #(key-signature::special-print `((-3 . ,magenta) (1 . ,cyan)))
  
  \key ces \major
  ces'1
  \key a \major
  a'1
  \key g \major
  g'1
}