tools/bazel prints color ANSI codes unconditionally.
This should only be done if the output is a color-capable terminal.
Bazel and gtest internally detects and adapts to this.

$ bazel run //src/mongo/dbtests:dbtest -- MockDBClientConnTest --runs=2 >out.txt 2>&1
$ vim out.txt
^[[0;32mINFO:^[[0m running wrapper hook... 
INFO: auto_header build generated: 614.4 ms ...

We shouldn't be seeing this noise in text files.

Detecting output terminal capabilities from a shell script might not be so easy.
An easy way forward is probably to just remove the color codes from the script.