% Author: Andrew Stacey
% http://tex.stackexchange.com/questions/14613
% A triangle with red, blue and green corners and weighted color within
% Based on fadings
\documentclass{article}
\usepackage{tikz}
\usepackage[active,tightpage]{preview}
\usepackage{subfig}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{5pt}%
\usetikzlibrary{fadings}
\pagestyle{empty}
\begin{document}
\begin{tikzpicture}
  \fill[green] (90:4) -- (210:4) -- (-30:4) -- cycle;
  \fill[blue,path fading=west] (90:4) -- (210:4) -- (-30:4) -- cycle;
  \fill[red,path fading=south] (90:4) -- (210:4) -- (-30:4) -- cycle;
\end{tikzpicture}
\end{document}