Message handler ignores the control characters in the output from external tools

I configured QtC to run this external tool, vale, which is a prose linter to check documentation blocks. The output from the tool is shown in the message pane at the bottom but the formatting is inconsistent between the different themes, and the output in Creator does not include the control characters added by the tool.

stdout you get on running vale in a bash shell:

The same thing presented by QtC in classic and design dark themes: