Python Tkinter How to remove the border around a Frame?
The first step is to set both the borderwidth and highlightthickness to zero. A frame has two border-like objects: the actual border and a "highlight ring". The latter is for showing that a frame has focus.
Once you do that, the frame will not have a border. If there's still some sort of border-like ring around the widget it is likely due to padding applied to the geometry manager, and what you are seeing is the color from the parent window.
In your specific case, since you are putting a label in the frame you need to turn the border of the label off, too. Most likely you are seeing the border of the label rather than the border of the frame.
I can't be any more specific since you didn't provide a minimal but otherwise fully working example that illustrates the problem.