What is the "Creating 1 swatches" info message ?

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Hello,

I was debugging my program and I kept seeing a message displayed by rviz : "Creating 1 swatches". With rqt_console here's what the message viewer says :

Node: /rviz
Time: 01:01:36.647000000 (1970-01-01)
Severity: Info
Published Topics: /initialpose, /move_base_simple/goal, /rosout

Creating 1 swatches

Location:
/tmp/binarydeb/ros-kinetic-rviz-1.12.15/src/rviz/default_plugin/map_display.cpp:MapDisplay::createSwatches:604

So I checked the MapDisplay (line 604). I'm not sure to really get what this is exactly (from my understanding it's not related to my issue it's simply the creation of the views in rviz).

Can someone explain it to me ?