\everymath could be used. This applies to
gather as well. To avoid coloring of inline math, you could check if you are within
align similar to amsmath's own checks.
\else \ifinalign@ \eqcolor
\centering $1 + \cos x$
As you can see, inline math is not colored. Regarding other displayed math: instead of
\[ ... \] you could use
gather*, respectively. This could be done in the preamble, without changes to equation environments in the text, such as