Menu: View→Interface Properties→Typefaces→Variable Names
Select a typeface for variable names.
All variable names are displayed with the same typeface, but each variable name can be displayed in a different font. See To change the font for a variable name.
Programming
In Amos Graphics programs, you can select the first item in this ComboBox as follows (Visual Basic):
Dim aComboBox As Windows.Forms.ComboBox = pd.GetComboBox("InterfacePropertiesForm", "ComboTypefaces_VariableNames")
aComboBox.SelectedIndex = 0