Cores

Conheça alguns pacotes que trabalham com cores no LaTeX.
xcolor
dvipsnames
svgnames

Carregue o pacote

\usepackage{xcolor}

Para dvipsnames digite

\usepackage[dvipsnames]{xcolor}



Para svgnames digite

\usepackage[svgnames]{xcolor}



Saiba ainda como definir novas cores que variam de 0 a 1 em rgb (minúsculo) e de 0 a 255 em RGB (maiúsculo).

Exemplo:

%\definecolor{orange}{rgb}{1,0.5,0} ou
\definecolor{orange}{RGB}{255,127,0}

Veja a seguir um exemplo simples e um outro com algumas cores do pacote:

\documentclass{article}
\usepackage[dvipsnames,svgnames,x11names]{xcolor}
\usepackage{tikz}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{5pt}%
\begin{document}
\begin{tikzpicture}[font=\tiny]
%\definecolor{orange}{rgb}{1,0.5,0} ou
 \definecolor{Orange}{RGB}{255,127,0}
  \fill[yellow] (0,0) rectangle ++(1.5,1);
  \fill[Orange] (1.6,0) rectangle ++(1.5,1); %dvipsnames
  \fill[OrangeRed] (3.2,0) rectangle ++(1.5,1); %svgnames
  \fill[LightSkyBlue] (4.8,0) rectangle ++(1.5,1); %x11names
  \node at (.75,1.2) {base color};
  \node at (2.35,1.2) {dvipsnames};
  \node at (4,1.2) {svgnames};
  \node at (5.6,1.2) {x11names};
  \node at (.75,.5) {yellow};
  \node at (2.35,.5) {Orange};
  \node at (4,.5) {OrangeRed};
  \node at (5.6,.5) {LightSkyBlue};
\end{tikzpicture}
\end{document}


\documentclass{article}
\usepackage[svgnames,dvipsnames,x11names]{xcolor}
\usepackage{tikz}
%\usetikzlibrary{calc}
%recorta a figura
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\begin{document}
\newcounter{x} %novo contador
\setcounter{x}{1} %valor inicial do contador
\newcounter{y} %novo contador
\setcounter{y}{0} %valor inicial do contador
\begin{tikzpicture}
%Títulos
 \foreach \ti in {base color,dvipsnames,svgnames,x11names}
 {
  \node at (\thex,1.5) {\ti};
  \pgfmathsetcounter{x}{\thex+2} %soma 1 no contador
  \setcounter{x}{\thex} %redefine o contador
 }
%Cores
 \foreach \cor in {blue,cyan,green,yellow,orange,red,magenta,purple}
 {
  \draw[fill=\cor] (0,-\they) rectangle ++(2,1) node[black,shift={(-1,-.5)}] {\cor};
  \pgfmathsetcounter{y}{\they+1} %soma 1 no contador
  \setcounter{y}{\they} %redefine o contador
 }
\setcounter{y}{0}%reinicia contador
 \foreach \cor in {BlueViolet,Aquamarine,GreenYellow,Goldenrod,Peach,RedOrange,Rhodamine,Purple}
 {
  \draw[fill=\cor] (2,-\they) rectangle ++(2,1) node[black,shift={(-1,-.5)}] {\cor};
  \pgfmathsetcounter{y}{\they+1}
  \setcounter{y}{\they}
 }
\setcounter{y}{0}%reinicia contador
 \foreach \cor in {DarkBlue,LightBlue,LawnGreen,SandyBrown,Salmon,Crimson,Magenta,Purple}
{
  \draw[fill=\cor] (4,-\they) rectangle ++(2,1) node[black,shift={(-1,-.5)}] {\cor};
  \pgfmathsetcounter{y}{\they+1}
  \setcounter{y}{\they}
 }
\setcounter{y}{0}%reinicia contador
 \foreach \cor in {Blue3,Cyan3,Green3,Yellow2,Orange2,Red3,Magenta2,Purple4}
 {
  \draw[fill=\cor] (6,-\they) rectangle ++(2,1) node[black,shift={(-1,-.5)}] {\cor};
  \pgfmathsetcounter{y}{\they+1}
  \setcounter{y}{\they}
 }
\end{tikzpicture}
\end{document}

\documentclass{article}
\usepackage{tikz}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{5pt}%
\begin{document}
\pgfdeclareverticalshading{rainbow}{100bp}
{color(0bp)=(red); color(25bp)=(red); color(35bp)=(yellow);
color(45bp)=(green); color(55bp)=(cyan); color(65bp)=(blue);
color(75bp)=(violet); color(100bp)=(violet)}
 \begin{tikzpicture}[shading=rainbow]
  \shade[shading angle=90] (0,0) rectangle +(5,1);
 \end{tikzpicture}
\end{document}