On entering a harbour or navigation from sea, the channel is marked with red to port (the left) and Green to starboard (the right). On return to sea it’s important to remember that the makers remain in the same place and so the red will be on the starboard side of the channel. Unless, of course, you are in the Americas (and a few other places) where they do it the other way around.
To simplify or confuse the issue dependent on your point of view, when viewed from sea, ALL port channel markers are cans (upright cylinders - nearly) and ALL starboard markers are conical, regardless of colour.