get

Gets all of the additive values.

• (send a-wx:add-colour get r g b) -> void
      r : boxed small integer
      g : boxed small integer
      b : boxed small integer

  The r box is filled with the additive value for the red component of the colour. The g box is filled with the additive value for the green component of the colour. The b box is filled with the additive value for the blue component of the colour.