The FXAA Injector just over staurates the colours and makes them look very unnatural, some people like this, personally I hate it. They also make the textures and image sharper, but this again makes it look unnatural and too sharp.
FXAA itself isnt that great, its quite a power hog compared to SMAA which looks better and cuts less fps.
(you can get the SMAA injector without all the colour changing crap)
Get a better graphics card and use 4xMSAA, pixel perfect sharpness.