
plgcolbga:  Returns the background color (cmap0[0])  by 8-bit RGB value and double alpha transparency value 

DESCRIPTION:

    This function is used in example 31. 

SYNOPSIS:

plgcolbga(r, g, b, alpha)

ARGUMENTS:

    r (PLINT *, output) :    Pointer to an unsigned 8-bit integer (0-255)
    representing the degree of red in the color. 

    g (PLINT *, output) :    Pointer to an unsigned 8-bit integer (0-255)
    representing the degree of green in the color. 

    b (PLINT *, output) :    Pointer to an unsigned 8-bit integer (0-255)
    representing the degree of blue in the color. 

    alpha (PLFLT *, output) :     Pointer to PLFLT alpha transparency
    value. 
