How to substitute all hues of a color?

[miqmiq]

Hello, the attached capture is an expansion at the pixel level, I would like to change all the pixels with that different hues of beige in the complete image to grey #999999 for example. 

This is from an old and aged image of a book dust jacket, I am trying to erase the "paper" background in the image and then put a layer with a clean "paper", I made a bucket fill of that background paper with #999999 with the intention of at the end to change that color for transparency, but as you can see in the image are still a lot of pixels with different hues of beige left, so, is there any method/s to substitute all that different beige-ish pixels, or erase them, or make them transparent? 

Thank you.

[PixLab]

(08-29-2022, 01:38 AM)miqmiq Wrote: I made a bucket fill of that background paper with #999999 with the intention of at the end to change that color for transparency, but as you can see in the image are still a lot of pixels with different hues of beige left, so, is there any method/s to substitute all that different beige-ish pixels, or erase them, or make them transparent? 

Why not make these directly transparent, instead of coloring them, them make them transparent....

Colors ➤ Color to Alpha, a window opens, sample the color on your image, play with sliders

   

Please ➤ ext time, upload the original or a part of it as well, but not a "thing" ultra pixelated were you already did something, it will allow us to know about what we are working on and on a non degraded image  

[miqmiq]

Thank you very much Sir, you spared me a lot of work, I owe you one.