The Category Colour folders creates after I assign colour category in Rules option. I previous versions it only make colour box after the subject line and optionally subject line was able to be in same category colour , which was fine. Now it is also creates separate folder for every ruled colour category and even when I make it hiden or delete it still appears on other email clients - i.e. android phone. Can this option be turned off?
this is a side-effect of the new way we treat Gmail labels.
On Gmail a LABEL is a category that you can assign to a message but it also created that folder where you can then filter these messages. More labels can be assigned to one message. To read about Gmail labels check their support post here. Our blog post about adapting the server behaviour can be found here.
So, as long as you have a message with that category in your Gmail account, there will be a new folder created for it.
This cannot be turned off.
I’d suggest making these categories as Subfolders to another folder so you can at least not have them between your main mail folders.