it seems no matter how i try to save the file in Infranview with 96dpi, it lightens the shade.
You are very likely being bitten by the dreaded gAMA chunk.

That is: some software saves PNGs with embedded gamma-curve colour correction information in an attempt to match colours over different systems. Unfortunately, operating systems commonly in use don't really do colour correction, so attempts to apply gamma in this fashion result in results which are not only wrong, but inconsistent. In particular, PNGs saved with a gAMA chunk cannot be made to match a colour set in HTML or CSS on all browsers. For the web, you should always save your PNGs without any gamma information.

Xtreme has done the right thing and saved your 'logo_PROD' without gamma. However the original image - and hence presumably all the other images which are supposed to match it - have been exported with a gAMA by some other misguided tool, and this will, in some circumstances, operating systems, settings and browsers, cause inconsistent results. For what it's worth the colours match on my current setup, but that's by pure luck.

You should go through your existing PNGs and re-export them with gamma turned off to match both the Xtreme-exported image and other colours on the page. I don't know if Irfan gives you that option; if not, I personally use GIMP. You could also do it in a batch method using something like pngcrush.