Newbie question about casting literals - oracle/postgres

Ok,

I have a query that runs fine in oracle:

select driver_id, 'GREEN' as color, pos_date, pos_lat, pos_lon
from driver_pos
where driver_id = 1
order by pos_date

The only way this works in postgres is by casting 'GREEN' to text using
'GREEN'::text

The problem is then this does not work with oracle. Since my software
has to support both databases, I am left in a bit of a bind. Any ideas
on how to make postgres accept 'GREEN' as text without my having to
spell it out by casting?

Thanks!
naeem