2.1.1282 Part 1 Section 18.104.22.168, alphaInv (Alpha Inverse Effect)
a. The standard does not include information on the optional color element.
In Office, other color channels are modified only if a color is specified. If a color is specified, all effect colors are replaced by the constant color value and the alpha values are inverted. If no color is specified, only the alpha values are modified and the other color channels are unchanged.