It turns out I made a little mistake. The regex should be more like ^[A-Fa-f0-9]+$. The "0" problem might be sorted like this ^[A-Fa-f1-9][A-Fa-f0-9]*$.
I lead the Chrome Developer Relations team at Google.
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Our team tries to make it easier for developers to build on the web by supporting every Chrome release, creating great content to support developers on web.dev, contributing to MDN, helping to improve browser compatibility, and some of the best developer tools like Lighthouse, Workbox, Squoosh to name just a few.