How to make a tkinter Label background transparent?

I have a window with a label as my frame. I did this because i wanted an image in the background. But now im having trouble with the other labels i have used. The other labels i have used to actually labeled things dont have a transparent background. Is there a way to make the background of these labels transparent?

OpenCV: Choosing HSV thresholds for color filtering

In order to filter a color out of an image, it’s necessary to set boundaries as to which color needs to be detected. I have a feeling this is mostly a trial-and-error process. Are there any ways to quickly find the correct thresholds for a particular color? In this specific case I’m trying to detect the gray area of the graph in the picture below. This without detecting the dotted lines of course. For this example I need very specific boundaries. The question is, how can I find them easily?