Display how the alpha transparency for rgb() varies.
testAlpha(alpha=seq(0,1,len=25), fg="blue", bg="yellow",
border="black", grid=FALSE, ...)numeric vector of alpha transparency values values from 0 to 1.
foreground colour of the top shape that varies in transparency.
background colour (remains constant) of the underlying shape.
border colour (which also changes in transparency) of the foreground polygon.
logical: if TRUE, lay a grey grid on the background colour.
additional graphical arguments to send to the the ploting functions.
Invisibly returns the compound RGB matrix for fg, alpha,
bg, and border.