# Filling in markers in pgfplots

I've been searching around and digging through the pgfplots manual and I can't quite seem to find a good answer for this. I'm trying to make a graph with "open circles" to indicate where the function is undefined. Right now I'm using the following:

\begin{tikzpicture}
\begin{axis}[
domain=-2:6,
xtick={-2,...,6},
ytick={-20,-10,...,40},
xmajorgrids=true,ymajorgrids=true,
xlabel={$x$},title={Graph of $y=g(x)$}
]
\addplot+[only marks,mark=o,mark options={scale=2},text mark as node=true] coordinates {
(-2,-20)
(6,40)
(5,10)
};
\end{axis}
\end{tikzpicture}


This results in the following picture:

Is there a simple way to fill in those circles so we don't see the graph behind them? I've tried adding "fill=white", "fill opacity=0", etc to the "mark options", but to no avail. I've also tried using the tikz command \draw to manually draw a circle, but that didn't seem to work either.

Thanks!

mark=o is an unfilled circle. Use mark=* instead:

 \documentclass{standalone}

\usepackage{pgfplots}

\begin{document}
\begin{tikzpicture}
\begin{axis}[
domain=-2:6,
xtick={-2,...,6},
ytick={-20,-10,...,40},
xmajorgrids=true,ymajorgrids=true,
xlabel={$x$},title={Graph of $y=g(x)$}
]