\documentclass{article}
\usepackage[dvipsnames]{color}
\begin{document}

\section{Predefined colors}
{\color{black} Black} vs. \textcolor{black}{Black}.

{\color{white} White} vs. \textcolor{white}{White}.

{\color{red} Red} vs. \textcolor{red}{Red}.

{\color{green} Green} vs. \textcolor{green}{Green}.

{\color{blue} Blue} vs. \textcolor{blue}{Blue}.

{\color{cyan} Cyan} vs. \textcolor{cyan}{Cyan}.

{\color{magenta} Magenta} vs. \textcolor{magenta}{Magenta}.

{\color{yellow} Yellow} vs. \textcolor{yellow}{Yellow}.

\section{RGB colors}
\definecolor{rgbred}{rgb}{1.0,0.0,0.0}
{\color[rgb]{1.0,0.0,0.0} Red}
vs. \textcolor[rgb]{1.0,0.0,0.0}{Red}
vs. \textcolor{rgbred}{Red}.

\section{CMYK colors}
\definecolor{cmykcyan}{cmyk}{1.0,0.0,0.0,0.0}
{\color[cmyk]{1.0,0.0,0.0,0.0} Cyan}
vs. \textcolor[cmyk]{1.0,0.0,0.0,0.0}{Cyan}
vs. \textcolor{cmykcyan}{Cyan}

\definecolor{cmykblack}{cmyk}{0.0,0.0,0.0,1.0}
{\color[cmyk]{0.0,0.0,0.0,1.0} Black}
vs.\textcolor[cmyk]{0.0,0.0,0.0,1.0}{Black}
vs.\textcolor{cmykblack}{Black}

\section{Gray colors}
\definecolor{grayblack}{gray}{0.0}
{\color[gray]{0.0} Black}
vs. \textcolor[gray]{0.0}{Black}
vs. \textcolor{grayblack}{Black}

\definecolor{gray}{gray}{0.5}
{\color[gray]{0.5} Gray}
vs. \textcolor[gray]{0.5}{Gray}
vs. \textcolor{gray}{Gray}

\definecolor{light}{gray}{0.9}
{\color[gray]{0.9} Light}
vs. \textcolor[gray]{0.9}{Light}
vs. \textcolor{light}{Light}


\section{Boxes}

\colorbox{gray}{\textcolor{light}{Light within Gray}}

vs. \colorbox[gray]{0.5}{\textcolor{light}{Light within Gray}}

\fcolorbox{blue}{red}{\textcolor{green}{Green in Red surrounded by Blue}}

\fcolorbox[cmyk]{0,1,0,0}{1,0,0,0}{\textcolor[cmyk]{0,0,1,0}{Yellow in Cyan surrounded by Magenta}}

\section{Math}
\[ \textcolor{red}{R} + \textcolor{green}{G} + \textcolor{blue}{B} \]

\[ \colorbox{red}{R} + \colorbox{green}{G} + \colorbox{blue}{B} \]

\[ \fcolorbox{green}{blue}{\textcolor{red}{R}} + \fcolorbox{blue}{red}{\textcolor{green}{G}} + \fcolorbox{red}{green}{\textcolor{blue}{B}} \]

\section{Named colors (DVIPS)}
\definecolor{myjunglegreen}{named}{JungleGreen}
{\color[named]{JungleGreen} JungleGreen}
vs. \textcolor[named]{JungleGreen}{JungleGreen}
vs. \textcolor{myjunglegreen}{JungleGreen}
% but NOT {\color{JungleGreen} JungleGreen}

\def\colorrow#1{\textcolor[named]{#1}{#1}&\colorbox[named]{#1}{#1}}
\begin{tabular}{ll|ll}
\colorrow{GreenYellow}&
\colorrow{Yellow}\\
\colorrow{Goldenrod}&
\colorrow{Dandelion}\\
\colorrow{Apricot}&
\colorrow{Peach}\\
\colorrow{Melon}&
\colorrow{YellowOrange}\\
\colorrow{Orange}&
\colorrow{BurntOrange}\\
\colorrow{Bittersweet}&
\colorrow{RedOrange}\\
\colorrow{Mahogany}&
\colorrow{Maroon}\\
\colorrow{BrickRed}&
\colorrow{Red}\\
\colorrow{OrangeRed}&
\colorrow{RubineRed}\\
\colorrow{WildStrawberry}&
\colorrow{Salmon}\\
\colorrow{CarnationPink}&
\colorrow{Magenta}\\
\colorrow{VioletRed}&
\colorrow{Rhodamine}\\
\colorrow{Mulberry}&
\colorrow{RedViolet}\\
\colorrow{Fuchsia}&
\colorrow{Lavender}\\
\colorrow{Thistle}&
\colorrow{Orchid}\\
\colorrow{DarkOrchid}&
\colorrow{Purple}\\
\colorrow{Plum}&
\colorrow{Violet}\\
\colorrow{RoyalPurple}&
\colorrow{BlueViolet}\\
\colorrow{Periwinkle}&
\colorrow{CadetBlue}\\
\colorrow{CornflowerBlue}&
\colorrow{MidnightBlue}\\
\colorrow{NavyBlue}&
\colorrow{RoyalBlue}\\
\colorrow{Blue}&
\colorrow{Cerulean}\\
\colorrow{Cyan}&
\colorrow{ProcessBlue}\\
\colorrow{SkyBlue}&
\colorrow{Turquoise}\\
\colorrow{TealBlue}&
\colorrow{Aquamarine}\\
\colorrow{BlueGreen}&
\colorrow{Emerald}\\
\colorrow{JungleGreen}&
\colorrow{SeaGreen}\\
\colorrow{Green}&
\colorrow{ForestGreen}\\
\colorrow{PineGreen}&
\colorrow{LimeGreen}\\
\colorrow{YellowGreen}&
\colorrow{SpringGreen}\\
\colorrow{OliveGreen}&
\colorrow{RawSienna}\\
\colorrow{Sepia}&
\colorrow{Brown}\\
\colorrow{Tan}&
\colorrow{Gray}\\
\colorrow{Black}&
\colorrow{White}\\
\end{tabular}
\end{document}

