How to add legend to pgfplots "contour prepared" plot?

Question

I want to add a legend to a pgfplots contour plot that is generated using the contour prepared option. The legend should contain the colors of the various levels and show the value associated with a given level. This post suggests a way that originally did not work (in 2013) but I assume should work in the current version of pgfplots. However, the output only lists one legend entry and not two.

Here is the MWE:

\documentclass[border=5mm]{standalone}
\usepackage{tikz,pgfplots}
\pgfplotsset{compat=1.12}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
  xmin=0.0,xmax=1.0,ymin=0.0,ymax=1.0,
  legend image post style={
    sharp plot,
    draw=\pgfkeysvalueof{/pgfplots/contour/draw color},
  },
  legend entries={foo,bar}]
  \input{data.tex}
\end{axis}
\end{tikzpicture}
\end{document}

The file data.tex contains the following:

\addplot[contour prepared={labels=false}]
table {
 0.1 0.9 1.0
 0.9 0.2 1.0

 0.1 0.8 0.1
 0.9 0.1 0.1
};

The data is contained in a separate file because in my real application the isolines are computed by a separate code. I kept it like this because I don't know whether this will make a difference as far as the legend is concerned. The output of the two files above is:

So there appear to be two problems:

1. It only shows "foo".
2. The color is black and not red.

What I would like to get is (produced with plot table, so not a contour plot):

Answer 1

Here are two ways, both using contours prepared, the first one with automatic colors, the second one with explicitly defined colors.

Contour prepared (automatic colors)

The data.tex file looks like this. Adding the + solved the issue when using color list name

\addplot+[contour prepared={labels=false}]
table {
    0.1 0.9 1.0
    0.9 0.2 1.0
};
\addplot+[contour prepared={labels=false}]
table {
    0.1 0.8 0.1
    0.9 0.1 0.1
};

And here's the code:

\documentclass[border=5mm]{standalone}
\usepackage{pgfplots}

\pgfplotsset{compat=1.12}

\begin{document}
\begin{tikzpicture}
\begin{axis}[
    xmin=0.0,xmax=1.0,ymin=0.0,ymax=1.0,
    cycle list name=color list,
    legend entries={foo, bar}
  ]

\input{data.tex}
\end{axis}
\end{tikzpicture}
\end{document}

Contour prepared (with explicit colors)

The data.tex file is as follows:

\addplot[contour prepared={draw color=red,labels=false}]
table {
 0.1 0.9 1.0
 0.9 0.2 1.0
};
\addplot[contour prepared={draw color=blue,labels=false}]
table {
 0.1 0.8 0.1
 0.9 0.1 0.1
};

Then the file will contain:

\documentclass[border=5mm]{standalone}
\usepackage{tikz,pgfplots}
\pgfplotsset{compat=1.12}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
    xmin=0.0,xmax=1.0,ymin=0.0,ymax=1.0,
    legend image post style={
        sharp plot,
        draw=\pgfkeysvalueof{/pgfplots/contour/draw color},
    },
    legend entries={red, blue}
  ]

\input{data.tex}
\end{axis}
\end{tikzpicture}
\end{document}