Can I see Uranus and Neptune with an iOptron telescope with a 600mm focal length. If so, can I expect to see them in colour, or simply as white objects?
Yes, you can.
I use a Newtonian reflector, 200mm objective, 1000mm focal length.
Uranus is sometimes right on the fringe of naked eye but looks a lot clearer as a small but recognisable blueish disc.
Neptune, sadly, just looks like a star to me ... but you can find it.