Unable to apply a color scheme via form designer

Thank you,

I would also like to change the design "Color Scheme" to the fourth option (green). However, it takes forever to save and never stops loading. What is causing that issue?

It seems that the issue is caused by some hidden widget at the end of your form. Please try removing the following widget and then checking the form in designer again.

The widget was most likely used by original form, if your form is a clone of some theme/template.