message: doc: allow null for foreground/background in schema
  Closes
diff: },
  "background": {
  "$ref": "#/definitions/Color",
  - "description": "Sets the background color of the profile. Overrides background set in color scheme if colorscheme is set. Uses hex color format: \"#rrggbb\". Default \"#000000\" (black)."
  + "description": "Sets the background color of the profile. Overrides background set in color scheme if colorscheme is set. Uses hex color format: \"#rrggbb\". Default \"#000000\" (black).",
  + "type": ["string", "null"]
  },
  "backgroundImage": {
  "description": "Sets the file location of the Image to draw over the window background.",
  },
  "foreground": {
  "$ref": "#/definitions/Color",
  - "description": "Sets the foreground color of the profile. Overrides foreground set in color scheme if colorscheme is set. Uses hex color format: \"#rrggbb\". Default \"#ffffff\" (white)."
  + "description": "Sets the foreground color of the profile. Overrides foreground set in color scheme if colorscheme is set. Uses hex color format: \"#rrggbb\". Default \"#ffffff\" (white).",
  + "type": ["string", "null"]
  },
  "guid": {
  "$ref": "#/definitions/ProfileGuid",
  