
plscolbga: Set the background color by 8-bit RGB value and double alpha value. 

DESCRIPTION:

    This function is used in example 31. 

SYNOPSIS:

plscolbga(r, g, b, a)

ARGUMENTS:

    r (PLINT, input) :      Unsigned 8-bit integer (0-255) representing the
    degree of red in the color. 

    g (PLINT, input) :      Unsigned 8-bit integer (0-255) representing the
    degree of green in the color. 

    b (PLINT, input) :      Unsigned 8-bit integer (0-255) representing the
    degree of blue in the color. 

    a (PLFLT, input) :      double value (0.0-1.0) representing the alpha
    value of the color. 
