But please don't ask me what is going on here...
Well... following is a definition of five strong points of interpolation curve - from pure grey to final color.
foreground-image-transformation: color-schema(darksalmon,salmon,lightsalmon,peachpuff,antiquewhite);pixels which are not grey are not converted. That red ball is it. Use this feature when you will want to show the same image in different states.