Luis, the images you provided are not really comparable. The first 2 (Browser, Original) are obviously screenshots and tagged with the monitor profile of your Mac (Cinema Display (D50 G1.8 A53.21). The third one has a sRGB profile. Colors therefore are different in this case.
If you want evaluate colors in a real comparable situation download this file:
https://dl.dropboxusercontent.com/u/7046655/Sample.zip
and double-click to unzip it.
You will find there:
• an original image (png format)
• a Muse file with this picture placed
• a folder with the HTML output of Muse
Now open the "index.html" in your browser and save the image (no screenshot please, but saving it by right click -> "save")
Open the saved image in photoshop, open the original image in Photoshop and open the image, Muse has outputted into "HTML/Images" in Photoshop as well.
You will see: There is definitely no visible and no measurable difference between the images.
That means: Muse does it right!
