This is the visual definition icon responsible for specifying how Thermodynamic diagram curves are displayed. It controls features such as line colour, style and thickness and how missing data will be plotted.
From Macro/Python the icon can be called as
The Thermo Plotting Editor
All of the parameters in this editor come directly from Magics, and are documented on the graph plotting reference page. Note that this editor contains only a subset of the whole range of parameters available on the graph plotting editor. Also, the parameters names' suffix are Thermo Temperature and Thermo Dewpoint, instead of Graph.