Sets the color key (transparency range) for a specified category on a GdPicture image. 

This function sets the high and low color-key values so that a range of colors can be made transparent. 

Any color that has each of its three components (red, green, blue) between the corresponding components of the high and low color keys is made transparent.

public GdPictureStatus SetColorKey(
    int ImageID, 
    Color ColorLow, 
    Color ColorHigh
);

Public Function SetColorKey(
    ByVal ImageID As Integer, 
    ByVal ColorLow As Color, 
    ByVal ColorHigh As Color
) As GdPictureStatus

A member of the GdPictureStatus enumeration.