For Misty's Place, the green and red markers are the area of the channel where you can expect deeper water below. The markers though can be used to signify an area you can land at and take off at.
For mariners, the rule is "Red right returning" or more details here:
http://www.boatingbasicsonline.com/content/general/6_3.phpLateral Buoys and waterway markers
In the International system, navigation aids mark the edges of channels to tell which way open water is. They are called day beacons if unlighted, lights if lighted at night, or buoys if they are floating. Some buoys are also lighted for identification at night.
"Red, Right, Returning" tells you to leave the red markers to your right, or starboard, when returning from sea. The green markers are then left on your port side and between is the channel. Be sure to look behind you when navigating a narrow channel to make sure you are not being pushed out by wind or current.
Floating Red markers are called nuns and are triangular in shape. They are numbered with even numbers. Floating Green markers, on the other hand, are called cans and are square or shaped like a large can and carry odd numbers.