A simple Chrome extension that optionally sets a per-project user-defined background color on the Google Cloud Console project switcher. You can install it in your browser from the Chrome store page.
The motivation for this extension -- apart from the pleasure I took in developing it -- is to avoid errors due a project mismatch, by letting users visually highlight specific projects, or project classes.
A possible future addition will be to implement regex-based highlighting rules.
Disclaimer: I'm currently working at Google, but this of course is not an officially supported Google product.