\HeaderA{rgb}{RGB Color Specification}{rgb}
\keyword{color}{rgb}
\begin{Description}\relax
This function creates colors corresponding to the given
intensities (between 0 and \code{max}) of the red, green and blue
primaries.

An alpha transparency value can also be specified
(0 means fully transparent and \code{max} means opaque).
If \code{alpha} is not specified, an opaque colour is generated.

The names argument may be used to provide names for the
colors.

The values returned by these functions can be used with a
\code{col=} specification in graphics functions or in \code{\LinkA{par}{par}}.
\end{Description}
\begin{Usage}
\begin{verbatim}
rgb(red, green, blue, alpha, names = NULL, maxColorValue = 1)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{red, blue, green, alpha}] numeric vectors with values in \eqn{[0, M]}{}
where \eqn{M}{} is \code{maxColorValue}.  When this is \code{255}, the
\code{red}, \code{blue}, \code{green}, and \code{alpha}
values are coerced to integers in \code{0:255} and the result is
computed most efficiently.
\item[\code{names}] character. The names for the resulting vector.
\item[\code{maxColorValue}] number giving the maximum of the color values
range, see above.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
The colors may be specified by passing a matrix or dataframe as argument
\code{red}, and leaving \code{blue} and \code{green} missing.
In this case the first three columns of \code{red} are taken to be
the \code{red}, \code{green} and \code{blue} values.

Semi-transparent colors (\code{0 < alpha < 1}) are supported only on
some devices: at the time of writing on the \code{\LinkA{pdf}{pdf}},
\code{windows}, \code{quartz} and \code{X11(type="cairo")} devices and
associated bitmap devices (\code{jpeg}, \code{png}, \code{bmp},
\code{tiff} and \code{bitmap}). They are supported by several
third-party devices such as those in packages \pkg{Cairo},
\pkg{cairoDevice} and \pkg{JavaGD}.  Only some of these
devices support semi-transparent backgrounds.

Most other graphics devices plot semi-transparent colors as fully
transparent, usually with a warning when first encountered.
\end{Details}
\begin{Value}
A character vector with elements of 7 or 9 characters, \code{"\#"}
followed by the red, blue, green and optionally alpha values in
hexadecimal (after rescaling to \code{0 ... 255}).
\end{Value}
\begin{SeeAlso}\relax
\code{\LinkA{col2rgb}{col2rgb}}for translating \R{} colors to RGB vectors;
\code{\LinkA{rainbow}{rainbow}}, \code{\LinkA{hsv}{hsv}}, \code{\LinkA{hcl}{hcl}},
\code{\LinkA{gray}{gray}}.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
rgb(0,1,0)

rgb((0:15)/15, green=0, blue=0, names=paste("red",0:15,sep="."))

rgb(0, 0:12, 0, max = 255)# integer input

ramp <- colorRamp(c("red", "white"))
rgb( ramp(seq(0, 1, length = 5)), max = 255)
\end{ExampleCode}
\end{Examples}

