change background color in selected rectangle

[IrfanUserGuyxyx]

At the IrfranView website https://www.irfanview.com/ you can download all the plugins. Click Plugins below either the 32 or 64 bit download. Get the "IrfanView All Plugins - 32-bit Windows Installer
". It should install them by running the download.

[oldtimer]

OK Thanks. I have downloaded "all" the plugins, which should include any needed to replace background color in selected area. I have chosen the old and new colors from the image itself as instructed. And nevertheless "Apply to image" still does nothing at all.

[Bhikkhu Pesala]

What did you choose for the Tolerance value? JPG and WebP images will not use the exact same colour values for every pixel in the background. Zoom in close and you can see the individual pixels. Try with different values for the tolerance.

[oldtimer]

I was using zero for tolerance value.

[oldtimer]

Yes, that was it! I started with tolerance of 6 and gradually increased the value. When I reached 40 the entire rectangle had the color I wanted. At last! Well, thanks to you, I am learning.