Colour / Gamma difference

I’ve attached an image to show the problem between a PC build and an HTML5 build. This happens in any browser that I test it in, it’s much brighter, has less contrast and the colours are slightly different. I’m guessing that this is because of differences in the post-process effects. Which post effects work with HTML5, and is there any other reason (gamma perhaps) that will be affecting only the HTML5 build?

Difference between two images. good effect.