Concatenate all the string values returned by distinct()

UPDATE / NOTE ON ANSWERS BELOW pg_typeof() on my target column was "regtype", not "text"...

So the contrived example below was a red herring. it WAS answered correctly by @richyen below. For those whose tables are NOT text, converting to text is needed, which is the accepted answer by @a_horse_with_no_name below

From table myschema.thing:

id | fruit  | color  | owner_id
---+--------+--------+---------
1  | apple  | red    |   100
2  | banana | yellow |   100
3  | tomato | red    |   500
4  | grape  | purple |   200

I'm trying to get the result:

colors
------------------
red,yellow,purple

Based on this page: https://www.postgresql.org/docs/11/functions-string.html

I've tried this:

select concat_ws(',', distinct(color)) as colors 
from myschema.thing

But it doesn't work. Where am I going wrong? Thanks in advance.

Solution

User string_agg()

select string_agg(distinct color::text, ',') as colors
from thing

Online example: https://rextester.com/GLFXG32756