It appears to be a bug. I created https://liquibase.jira.com/browse/CORE-1800 to track the fix. For now, you will have to fall back to the <sql> tag and define it yourself (either in the table creation or in an add check constraint statement).
Or you could use something like <modifySq><replace value="colors text" with="colors text CHECK (colors = ANY (ARRAY['red'::text, 'yellow'::text, 'blue'::text]))"/></modifySql> in your create table changeSet.
Nathan