This ensures that color picks that have multiple issues will
have them all checked at the same time, including ensuring that
the fix for one issue doesn't cause another issue.
Handling of the onError action has been changed from being called
at once to collecting the potential errors in a HashSet to deduplicate
them and then calling onError after a valid color has been found.
(Otherwise you would in the worst case get 256 error messages logged!)
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