Gimp script to "colorize" image

overlay.scm

(define (overlay filename filename2)
   (let* ((image (car (gimp-file-load RUN-NONINTERACTIVE filename
filename)))
          (drawable (car (gimp-image-get-active-layer image))))

          (gimp-brightness-contrast drawable 0 -127)
          (gimp-brightness-contrast drawable 0 127)

          (plug-in-colorify RUN-NONINTERACTIVE image drawable "#3498db")
          (gimp-image-convert-indexed image 0 0 255 0 0 "")

     (gimp-file-save RUN-NONINTERACTIVE image drawable filename2
filename2)
     (gimp-image-delete image)))