Colorado.
If it was a primary, the candidate picks watchers. For a general election, the *party* picks watchers.
Here’s the Colorado law for election watchers:
...”Watcher” means an eligible elector other than a candidate on the ballot who has been selected by a political party chairperson on behalf of the political party
by a party candidate at a primary election,
by an unaffiliated candidate at a general, congressional vacancy, or nonpartisan election, or by a person designated by either the opponents or the proponents in the case of a ballot issue or ballot question.
If selected by a political party chairperson, a party candidate, or an unaffiliated candidate, the watcher shall be affiliated with that political party or unaffiliated as shown on the registration books of the county clerk and recorder...
https://www.sos.state.co.us/pubs/elections/watcherPanel/files/ElectionWatchers-StatutesRules.pdf