I think the conflict is in your script, perhaps they changed something with Iris in the last WordPress update. If you remove line 1203 from input.js $input.trigger('change'); then the color picker works as expected: I don’t know if this has any impact on anything else, but it may help you look further.
event.returnValue is only used in wp-auth-check.js and jQuery itself so I don’t think this is a related issue.
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