How do I make the text in the following figure white and center the figure?

Question

How do I make the text in the following figure white and center the figure?

%% LyX 1.6.9 created this file.  For more info, see http://www.lyx.org/.
%% Do not edit unless you really know what you are doing.
\documentclass[english]{article}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage{babel}
\usepackage{multicol}
\usepackage{tikz}

\begin{document}
\begin{center}
%
\begin{figure}
\caption{Overlap of valley regions in tumourigenic cell line vs. control}

\definecolor{darkColor}{rgb}{0.102,0,0.2} %darkPurple 
\definecolor{mediumColor}{rgb}{0.2,0,0.4} %purple 
\definecolor{lightColor}{rgb}{0.413,0.315,0.615} %lightPurple
\begin{tikzpicture}[scale=1]
\tikzstyle{LeftLabel}= [text=white]
\tikzstyle{RightLabel}= [text=white]
\tikzstyle{CenterLabel}= [text=white]
\def\firstcircle{(-1.25,0) circle (1.75)}
\def\secondcircle{(1.25,0) circle (1.75)}
 %\draw[help lines] (-4,-4) grid (8,4);
  \begin{scope}
\fill[lightColor] \firstcircle;
\fill[lightColor] \secondcircle;
\clip \firstcircle;
\fill[mediumColor] \secondcircle;
  \end{scope}
  \draw \firstcircle ;
  \draw (-1,0) node [left] (LeftLabel) {Cancer} ;
  \draw node[below of=LeftLabel, node distance=.4cm] {1710};
  \draw \secondcircle ; 
  \draw (1,0) node [right] (RightLabel) {Control};
  \draw node[below of=RightLabel, node distance=.4cm] {2180};
  \draw (0,0) node [] (overlap) {};
  \draw node[below of=overlap, node distance=.4cm] {373};
\end{tikzpicture}%

\end{figure}

\par\end{center}
\end{document}

Answer 1

Either add white to the node option or use text=white for the picture. Use \centering at the beginning of the figure. The \caption belongs below figures (but above tables).

\documentclass[english]{article}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage{babel}
\usepackage{multicol}
\usepackage{tikz}

\begin{document}
%
\begin{figure}
    \centering
\definecolor{darkColor}{rgb}{0.102,0,0.2} %darkPurple 
\definecolor{mediumColor}{rgb}{0.2,0,0.4} %purple 
\definecolor{lightColor}{rgb}{0.413,0.315,0.615} %lightPurple
\begin{tikzpicture}[scale=1,text=white]
\def\firstcircle{(-1.25,0) circle (1.75)}
\def\secondcircle{(1.25,0) circle (1.75)}
 %\draw[help lines] (-4,-4) grid (8,4);
  \begin{scope}
\fill[lightColor] \firstcircle;
\fill[lightColor] \secondcircle;
\clip \firstcircle;
\fill[mediumColor] \secondcircle;
  \end{scope}
  \draw \firstcircle ;
  \draw (-1,0) node [left] (LeftLabel) {Cancer} ;
  \draw node[below of=LeftLabel, node distance=.4cm] {1710};
  \draw \secondcircle ; 
  \draw (1,0) node [right] (RightLabel) {Control};
  \draw node [below of=RightLabel, node distance=.4cm] {2180};
  \draw (0,0) node [] (overlap) {};
  \draw node [below of=overlap, node distance=.4cm] {373};
\end{tikzpicture}%

\caption{Overlap of valley regions in tumourigenic cell line vs. control}
\end{figure}

\end{document}

---

Note that you also an use transparency (e.g. opacity option) so that the overlapping area gets automatically a different color. I would also use circle shaped nodes.

\documentclass[english]{article}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage{babel}
\usepackage{multicol}
\usepackage{tikz}

\begin{document}
%
\begin{figure}
    \centering
\definecolor{darkColor}{rgb}{0.102,0,0.2} %darkPurple 
\definecolor{mediumColor}{rgb}{0.2,0,0.4} %purple 
\definecolor{lightColor}{rgb}{0.413,0.315,0.615} %lightPurple
\begin{tikzpicture}[scale=1,text=white,font=\sffamily]
\def\firstcircle{(-1.25,0) circle (1.75)}
\def\secondcircle{(1.25,0) circle (1.75)}
  \node [fill=lightColor,draw=black,circle,minimum size=3.5cm,align=center,opacity=.666,text=white] at (-1.25,0)
  (Cancer) {Cancer\\1710};
  \node [fill=lightColor,draw=black,circle,minimum size=3.5cm,align=center,opacity=.666,text=white] at (+1.25,0)
    (Control) {Control\\2180};
  \path (Cancer) -- (Control) node [midway] {373};
\end{tikzpicture}%
\caption{Overlap of valley regions in tumourigenic cell line vs. control}
\end{figure}

\end{document}