Fix: Swapped colors in waterworld description (#1210)

Author: Zoraiyo

pettingzoo/sisl/waterworld/waterworld.py

@@ -33,7 +33,7 @@
 poison respectively. The number of features per sensor is 8 by default with `speed_features` enabled, or 5 if `speed_features` is turned off. Therefore with `speed_features` enabled, the observation shape takes the full form of `(8 × n_sensors) + 2`. Elements of the observation vector take on
 values in the range [-1, 1].
 
-For example, by default there are 5 agents (purple), 5 food targets (red) and 10 poison targets (green). Each agent has 30 range-limited sensors, depicted by the black lines, to detect neighboring entities (food and poison targets) resulting in 242 element vector of computed values about the
+For example, by default there are 5 agents (purple), 5 food targets (green) and 10 poison targets (red). Each agent has 30 range-limited sensors, depicted by the black lines, to detect neighboring entities (food and poison targets) resulting in 242 element vector of computed values about the
 environment for the observation space. These values represent the distances and speeds sensed by each sensor on the archea. Sensors that do not sense any objects within their range report 0 for speed and 1 for distance.
 
 This has been fixed from the reference environments to keep items floating off screen and being lost forever.