How to get array of unique array values across rows?

I have a field containing a set of codes in a varchar array, each tied to a
person.

client_id | integer |
service_codes | character varying(10)[] |

I'm trying to query this info so that I can get the list (presumably in an
array) of all the values in this array, across all the records for a
client. So that if a person has two records, one with ORANGE and BLUE, and
one with BLUE and GREEN, I could end up with a list of ORANGE, BLUE and
GREEN.

I had hopes for:

SELECT client_id,array_agg(service_codes) FROM foo GROUP BY client_id;

But was rebuffed with "ERROR: could not find array type for data type
character varying[]"

There's probably an easy answer for this, but it's completely escaping me.
Any help appreciated. Thanks.

Ken

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