Creates (and optionally draws) a grid frame grob representing a color
key that can be placed in other grid-based plots. Primarily used by
levelplot when a color key is requested.
draw.colorkey(key, draw = FALSE, vp = NULL)A list determining the key. See documentation for levelplot,
in particular the section describing the colorkey argument,
for details.
A scalar logical, indicating whether the grob is to be drawn.
The viewport in which to draw the grob, if applicable.
A grid frame object (that inherits from "grob")