Another note on this.
What is not working:
Changing the default fill color of paragraph shading, if you are changing the defaults of your "Basic Paragraph Style" when no document is open to "None" and proceed.
You still have a swatch named "C=100 M=0 Y=0 K=0" that is in use. I suspect, that fill color "C=100 M=0 Y=0 K=0" is part of the "invisible" "No Paragraph Style" paragraph style. And "Basic Paragraph Style" is based on "No Paragraph Style".
Just tested this by scripting (ExtendScript/JavaScript) and can confirm my assumption.
One can address the "No Paragraph Style" by the index of 0 of the paragraph styles collection of the app (that means InDesign) like that:
app.paragraphStyles[0].paragraphShadingColor.name;
will return "C=100 M=0 Y=0 K=0".
And one cannot change this. Even by scripting.
Trying to assign "None" to the paragraph shading color property as value
app.paragraphStyles[0].paragraphShadingColor = "None";
will throw an error.
So "C=100 M=0 Y=0 K=0" will stay with us for a long time, I suspect ;-)
Uwe