What to do with "unknown colors" showing up from external HTML

[nperez0111]

Describe the bug

When pasting in external HTML (or setting it via an initial document JSON). There can be textColor or backgroundColor which is a value other than the color names which we already support (e.g. red, blue, etc).

This is originally found to be an issue with this PR: #2179

To Reproduce

initialContent={ [ { type: "paragraph", props: { textColor: "rgba(0, 0, 0, 0.5)" } } ] }

By explicitly setting the textColor to an invalid value, it is preserved in the document when it should likely be stripped as invalid? Perhaps the zod props parsing introduced by #2096 will resolve this issue?

Misc

• Node version: N/A
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