在显示方程中应用颜色时，显示空间的上方和下方会发生变化

Question

尝试在显示方程中应用颜色，我刚刚从修改了环境amsmath.sty。应用颜色时，上方和下方的空间会被修改（增加空间），请参见下图，在第一个方程中，下方空间更多，而第二个方程上方空间更多。

如何修复提到的默认空间\abovedisplayskip \belowdisplayskip？

梅威瑟：

\documentclass{book}
\usepackage{amsmath,amsfonts,amssymb,color}

\makeatletter
\renewenvironment{equation}{\color{red}%
  \incr@eqnum
  \mathdisplay@push
  \st@rredfalse \global\@eqnswtrue
  \mathdisplay{equation}%
}{%
  \endmathdisplay{equation}%
  \mathdisplay@pop
  \ignorespacesafterend
}

\def\start@align#1#2#3{\color{red}%
    \let\xatlevel@#1% always \z@, \@ne, or \tw@
    \maxfields@#3\relax
    \ifnum\maxfields@>\m@ne
        \checkat@true
        \ifnum\xatlevel@=\tw@
            \xxat@true
        \fi
        \multiply\maxfields@\tw@
    \else
        \checkat@false
    \fi
    \ifingather@
        \iffalse{\fi\ifnum0=`}\fi
        \DN@{\vcenter\bgroup\savealignstate@\align@#2}%
    \else
        \ifmmode
          \if@display
             \DN@{\align@recover}%
          \else
            \nomath@env
            \DN@{\@namedef{end\@currenvir}{}\@gobble}%
          \fi
        \else
            $$%
            \let\split\insplit@
            \DN@{\align@#2}%
        \fi
    \fi
    \collect@body\next@
}

\makeatother


\begin{document}

text $inline equation a+b$
\[
a = b, \text{\qquad by assumption}
\]
Note the spacing command \qquad in the argument of \text. You could also
type
\[
a = b, \qquad \text{by assumption}
\]
because \qquad works in math as well as in text (see Sections 8.1 and B.9).
\begin{equation}\label{E:firstInt}
aa+bb \sin x \, dx = 2
\end{equation}
because \qquad works in math as well as in text (see Sections 8.1 and B.9).
\begin{equation}\label{E:firstInt}
\int_{0}^{\pi} \sin x \, dx = 2
\end{equation}

type the following, using as the line separator and \& as the alignment point:
\begin{align}
r^{2} &= s^{2} + t^{2}, \label{E:Pyth}\\
2u + 1 &= v + w^{\alpha}, \label{E:alpha}\\
x &= \frac{y + z}{\sqrt{s + 2u}};\label{E:frac}
\end{align}
is typed as follows:
$$
f(x)=
\begin{cases}
-x^{2}, &\text{if $x < 0$;}\\
\alpha + x, &\text{if $0 \leq x \leq 1$;}\\
x^{2}, &\text{otherwise.}
\end{cases}
$$
which is typed as
\begin{gather*}
\overleftarrow{a} \quad \overrightarrow{aa}\\
\overleftrightarrow{aaa} \quad \underleftarrow{aaaa}\quad
\underrightarrow{aaaaa} \quad \underleftrightarrow{aaaaaa}
\end{gather*}

This formula is typed as
\begin{multline}\label{E:mm2}
(x_{1} x_{2} x_{3} x_{4} x_{5} x_{6})^{2}\\
+ (y_{1} y_{2} y_{3} y_{4} y_{5}
+ y_{1} y_{3} y_{4} y_{5} y_{6}
+ y_{1} y_{2} y_{4} y_{5} y_{6}
+ y_{1} y_{2} y_{3} y_{5} y_{6})^{2}\\
+ (z_{1} z_{2} z_{3} z_{4} z_{5}
+ z_{1} z_{3} z_{4} z_{5} z_{6}
+ z_{1} z_{2} z_{4} z_{5} z_{6}
+ z_{1} z_{2} z_{3} z_{5} z_{6})^{2}\\
+ (u_{1} u_{2} u_{3} u_{4} + u_{1} u_{2} u_{3} u_{5}
+ u_{1} u_{2} u_{4} u_{5} + u_{1} u_{3} u_{4} u_{5})^{2}
\end{multline}


\end{document}