Hi Rich
Glad you got it fixed. I am assuming the the CTRL+left click was on the Layers thumbnail to select the pixels.
With that assumption, the problem you can have is when there is partial transparency in the image. I bet your original image had some partial transparency around the edges of the colored images and that remained in spite of other steps that might have been taken. When filled with white, that leave it looking grayish which is really just transparency looking through to the Layer underneath.
Transparency around the edges is pretty easy to get if you have feathering, antialiasing, or even sharpening around Text when done when the object is on a transparent background.
You would get the exact results you had.
Just a thought
John Wheeler
Filling a selection that is not 100% selected will retain some transparency at those edges