As stated here: Finding Exact Values, since the field has been analyzed when indexed – you have no way of exact-matching its tokens (“:”). Whenever the tokens should be searchable the mapping should be “not_analyzed” and the data needs to be re-indexed.
If you want to be able to easily match only “:feed:” inside the message field you might want to costumize an analyzer which doesn’t tokenize “:” so you will be able to query the field with a simple “match” query instead of wild characters.