Huecycle

Emacs package that lets faces change color when idle:

Features

First, define what faces will be affected with huecycle-set-faces:

(huecycle-set-faces
 ((background . mode-line)))

Then calling huecycle will then let those faces change color.

You can specify multiple faces into a group, which will allow settings to take affect for all faces. Groups follow the form of association list entries mapping a face spec to affected faces, followed by options.

(huecycle-set-faces
 ((background . mode-line)
  (foreground . (warning highlight))
  :speed 2.0
  :persist t))

Faces in a group sync up color changes.

You can have multiple groups, each with their own configurations:

(huecycle-set-faces
 ((background . hl-line)
  (foreground . (line-number-current-line))
  :random-color-hue-range (0.0 1.0)
  :random-color-saturation-range (0.8 1.0)
  :random-color-luminance-range (0.5 0.8))
 ((foreground . warning)
  :color-list ("#FF0000" "#FF0000" "#DDAAAA")
  :next-color-func huecycle-get-next-list-color
  :speed 5.0))

Read the documentation for huecycle-set-faces to see all the ways you control groups.

Usage

You can make Emacs huecycle when idle using M-x huecycle-when-idle.

You can specify how long Emacs will cycle for with M-x huecycle-set-cycle-duration.