There are dozens of good grain reduction filters for AviSynth. You will find lots of information at Doom9.org, but it might seem a little daunting at first.

My current favourite is MVDegrain2 (as discussed in this thread).

Colour saturation is easily adjusted by the internal filter Tweak(). If you want an easy to use GUI, I recommend AvsP.

List of stuff to download:
AviSynth (obviously)
DGMPGDec package (for reading MPEG-2 video into AviSynth)
MVTools (contains the above mentioned grain filter)
AvsP (for previewing scripts and adjusting parameters)