[Rd] undocumented 'offset' argument in src/library/grDevices/man/adjustcolor.Rd

[Ben Bolker]

   The 'offset' argument description is blank ...

   maybe 'additive adjustment to each of the (red, green, blue, alpha) 
values defining the colors, after adjustment by the corresponding 
\code{.f} factor' ...?

This is the relevant code:

  x <- col2rgb(col, alpha = TRUE)/255
     x[] <- pmax(0, pmin(1,
                         transform %*% x +
                         matrix(offset, nrow = 4L, ncol = ncol(x))))
     rgb(x[1L,], x[2L,], x[3L,], x[4L,])