Style to make axis tick label opaque using “extra y tick” feature

Question

This is a follow up to Style to make axis tick label opaque, where a suggestion was made to use the extra y ticks to specify special tick marks and use extra y tick style to apply a style to only those tick labels.

I attempted to adapt Jake's answer to the above referenced question and apply that by making -2 not a normal tick, but an extra y tick:

ytick={-1,1,2,3,4},%    Note: -2 not listed here
extra y ticks={-2},% 
extra y tick style={draw=none, inner sep=0pt, outer sep=0.3333em, fill=white, text opacity=1},

but this does not seem to have any effect on the y tick label at -2:

Code:

\documentclass{article}
\usepackage{pgfplots}

\newcommand{\XMin}{-2.2}%
\newcommand{\XMax}{1.5}%

\pgfkeys{/pgfplots/My Axis Style/.append style={
    width=7cm, height=8cm,
    xmin=\XMin, xmax=\XMax, ymin=-3.2, ymax=2.5,
    axis y line=center,
    axis x line=middle, 
    axis on top=true,
    ytick={-1,1,2},
    extra y ticks={-2},
    extra y tick style={draw=none, inner sep=0pt, outer sep=0.3333em, fill=white, text opacity=1},
    }
}

\newcommand*{\AddPlotFunction}{\addplot[smooth, ultra thick, domain=\XMin:\XMax, red]  {exp(x)-2} node [left] {$y=e^x-2$}}%
\newcommand*{\AddPlotAsymptote}{\addplot[smooth, thin,        domain=\XMin:\XMax, blue] {-2} node [below left] {$y=-2$}}%

\begin{document}
\begin{tikzpicture}
\begin{axis}[My Axis Style]
    \AddPlotFunction;
    \AddPlotAsymptote;
\end{axis}
\end{tikzpicture}
\end{document}

Answer 1

You need to supply the fill option to extra y tick style={y tick label style={<options>}}.

This is similar to how you need to supply it to y tick label style, not y tick style in case you're using "normal" ticks. Unfortunately, there's no every y tick label style, so you'll have to use y tick label style inside extra y tick style.

\documentclass{standalone}
\usepackage{pgfplots}

\newcommand{\XMin}{-2.2}%
\newcommand{\XMax}{1.5}%

\pgfplotsset{
    My Axis Style/.append style={
        width=7cm, height=8cm,
        xmin=\XMin, xmax=\XMax, ymin=-3.2, ymax=2.5,
        axis y line=center,
        axis x line=middle, 
        axis on top=true,
        ytick={-1,1,2},
        extra y ticks={-2},
        extra y tick style={
            y tick label style={
                fill=white,
                draw=none,
                inner sep=0pt,
                outer sep=0.3333em
            }       
        },
    }
}

\newcommand*{\AddPlotFunction}{\addplot[smooth, ultra thick, domain=\XMin:\XMax, red]  {exp(x)-2} node [left] {$y=e^x-2$}}%
\newcommand*{\AddPlotAsymptote}{\addplot[smooth, thin,        domain=\XMin:\XMax, blue] {-2} node [below left] {$y=-2$}}%

\begin{document}
\begin{tikzpicture}
\begin{axis}[My Axis Style]
    \AddPlotFunction;
    \AddPlotAsymptote;
\end{axis}
\end{tikzpicture}
\end{document}