Is it possible to make Swatches tab come as default not RGB
The underlying implementation there is a TabSheet. Maybe try setRGBVisibility(false) and setRGBVisibility(true)?
That might switch the order of the tabs
A built-in color picker definitely makes life easier for admin/config UIs. Until I added one properly, I used to grab HEX values from mockups/screenshots with https://colorpickerimage.org/ and paste them directly into the app settings. Simple workaround, but surprisingly useful when testing themes quickly.