So you created a frame on your master, filled it with a color.
Then you go in your document and placed the B&W picture in the colored frame.
The white in your B&W picture is actually the paper color, if you would print your B&W image on a colored paper there would be the color of the paper coming through, white can't be printed in a CMYK workflow.
The same applies for your problem: your frame is filled with a color so the white (which is the paper color) is replaced with the color in your frame.
If you want just black and white, don't fill the frame with a color.
hope this explains it
carlow