"Unknown named color" stops experiment running... [PARTIALLY SOLVED]

Thank you for your answer.

The field was left blank at the time, which worked fine running the experiment under the Builder (not on pavlovia however).

After browsing the forum, I changed the blank space to “$None”, but a message error stated that None was undefined.
Following How to make the fill color of a ShapeStim transparent I also tried “None”


I thought this was it, but I get the following error message :