How to specify a fill color in RGB format in a node in tikzpicture?

Question

I am just trying to get a rounded corner box with some text in it. The text color will be white and the box will be filled with a particular color.

The preamble includes:

\usepackage{tikz}
\usetikzlibrary{calc,trees,positioning,arrows,chains,shapes.geometric,%
decorations.pathreplacing,decorations.pathmorphing,shapes,%
matrix,shapes.symbols,plotmarks,decorations.markings,shadows}

The code I have used is:

\begin{tikzpicture}
\node[drop shadow,fill=black,draw,rounded corners]
{\textcolor{white}{TEST}};
\end{tikzpicture}

How can I specify an arbitrary color (RGB values in a range of 0-255) in the fill option?

Also, am I using too advanced a tool (tikz) to do something simple (draw a rounded corner rectangle filled with a color and text of some other color)?

Answer 1

In answer to your first question - mixing colours in (say) RGB format - you could use the notation similar to that specified in the xcolor package documentation, since TikZ recognizes this. For example, mixing/sharing proportions of black green is obtained using

\node[...,fill=black,...]
\node[...,fill=black!60!green,...]
\node[...,fill=black!30!green,...]
\node[...,fill=green,...]

and displays

Or, if you're interested in mixing certain quantities of RGB colours, you can use a part-wise mix as follows:

\node[...,fill={rgb:red,4;green,2;yellow,1},...]
\node[...,fill={rgb:red,1;green,2;blue,5},...]
\node[...,fill={rgb:orange,1;yellow,2;pink,5},...]
\node[...,fill={rgb:black,1;white,2},...]

which outputs

For answering your second question - dealing with boxes - you can use the fancybox package or even PStricks. Here is an example using the latter:

\documentclass{article}
\usepackage{pstricks}
\begin{document}
\begin{pspicture}(5,5)
  \psset{fillstyle=solid,framearc=.3}
  \psframebox[fillcolor=red]{\textcolor{white}{TEST}}
  \psframebox[fillcolor=green!50!red]{\textcolor{white}{TEST}}
  \psframebox[fillcolor=black!50]{\textcolor{white}{TEST}}
  \psframebox[fillcolor={rgb:red,1;green,2;blue,3}]{\textcolor{white}{TEST}}
\end{pspicture}
\end{document}​

Answer 2

One approach is to predefine in the preamble all colors one wants to use, for instance

\definecolor{mycolor}{rgb}{1,0.2,0.3}

with values in the interval (0,1) or

\definecolor{mycolor}{RGB}{255,51,76}

with integer values in the range 0–255 (use a more sensible name than mycolor) and then mycolor can be used in all color specifications, for instance

\node[drop shadow,fill=mycolor,draw,rounded corners]

In this way you can control the colors and also change them just by modifying their definition.

Answer 3

Werner has shown the rgb-syntax to mix colors, egreg has shown how to define a color in RGB and then use it. If you want to specify a color with RGB values [0-255] without defining it before, you can use the rgb-syntax Werner has shown by setting the optional div-parameter to 255 (see xcolor package documentation, pages 13 and 16).

\documentclass{article}
\usepackage{tikz}
\begin{document}
\tikz\node[rounded corners, fill={rgb,255:red,21; green,66; blue,128}, text=white, draw=black] {hello world};
\end{document}

Answer 4

Another approach, that builds on egregs answer, is to predefine the color one wants to use right before it is used. In that way one doesn't have to be so creative when coming up with the names for all colors, which is especially cumbersome if a lot of different colors have to be defined. The color can then be used in all color specifications (just like colors defined in the preamble), for instance

...
\definecolor{tempcolor}{rgb}{1,0.2,0.3}
\node[drop shadow,fill=tempcolor,draw,rounded corners]
...

with values in the interval (0,1) or

...
\definecolor{tempcolor}{RGB}{255,51,76}
\node[drop shadow,fill=tempcolor,draw,rounded corners]
...

with integer values in the range 0–255 (the name "tempcolor" is just a suggestion).

If you want to make sure you're not overriding any earlier defined color named tempcolor, you can always define the color in a separate scope:

...
{
    \definecolor{tempcolor}{rgb}{1,0.2,0.3}
    \node[drop shadow,fill=tempcolor,draw,rounded corners]
}
...