This is an onging issue ever since the launch of the play axis in scatter chart. Please fix it.
I have sent a email to consult this issue internally, will update here once I get any information.
Best Regards,Qiuyun Yu
I got information below:
This is a known limitation for now. There is a color-by-category toggle the user can apply that will give a unique color to each category grouping, even if there is no Legend field.
We hope to bring formatting parity to Play Axis later this year.