Bucket fill is tinting my entire image

[HavingTooMuchFun]

The upper image is the original; the bottom image is my attempt to bucket-fill with tan replacing the gray. This is very close to the minimum threshold to eliminate all of the dark gray, and as you can see, the tan that I bucket filled with is overlaying the white as well… not REPLACING the white, but mixing with it. This has happened recently with a variety of different images, with a variety of different colors both in the images and with the attempted bucket-fills; the result is as if I was looking at the image through tinted glasses, rather than the bucket fill just working on the selected color. I must have accidentally changed some sort of setting… does anyone have any idea what it might be?