This message is generated when the indicated expression is not a valid color or gray-level specification.
A valid color specification is an expression of the form RGBColor[r,g,b], Hue[h], Hue[h,s,b], or CMYKColor[c,m,y,k], where all of the arguments are positive real numbers.
A valid gray-level specification is an expression of the form GrayLevel[x], where x is a real number between zero and one.
Off[message] switches off the message; On[message] switches it on. For example: Off[General::color].