In the following example, the space after the red equation is much larger than the space after the black one.
\documentclass[12pt]{article}
\usepackage{xcolor}
\begin{document}
\[ a = b \]
The quick brown fox jumps over the lazy dog.
\color{red}
\[ a = b \]
\color{black}
The quick brown fox jumps over the lazy dog.
\end{document}
It appears to me that the presence of \color{black}
fools TeX
into thinking there is something on the line after the equation, so the paragraph break causes a spurious blank line before the text. Section 3.7 of grfguide mentions spacing problems, but doesn't really explain the situation. What is on the line after the red equation?
Note that there is already a question asking how to deal with this problem; I want to understand what is going on.
color
command. If you replace\color{black}
with, for example,\marginpar{test}
you get the same result, regardless of how much colour changing occurs.\inserts
there,\label
would put a\write
there, all these nodes can affect vertical positioning,trivlist
?