Python 2.7 with pip install csa
The default mask is evoked using full which can then be visualized as shown below

Since the default mask represents all-to-all connections This would imply that purple is the color for connections.
However oneToOne mask includes only self-connection. This is also visualized as below

Notice here that yellow is the color for connections.
Therefore either purple or yellow should be the color for connections. Not both. This might be because of the function show()
PS: This issue is persistent also for python 3.7