I added a coloured Label Definition under Status [purple]. Afterwards, I changed that colour [to grey] but the folder colours remain as purple. New assignments are the new colour, however. Even if I reset the folder, restart the machine, exit and start DOPUS the folder colour remains the old colour.
You probably have another label that's also purple.
There is no label with that purple colour right now. If a purple folder that should be grey is moved, it remains purple. And if it is reset, that works to restore it to default. But when it is again labelled as grey then it becomes purple again.
It seems to have been the use of grey as an icon colour, not sure why.
I can't reproduce that, but it might depend on the details of how you have configured the label (both definition and assignment) and the exact RGB values you used.