this excess colour bleeding is a phenomonen of FG. Each object 'radiates'/bleeds its colour onto another object which in turn illuminates the area around it.
select the shader in the hypershade and open Attribute editor for that shader. Under the standard Maya attributes you should see the MR attributes. open and decrease the value of the Irradiance colour. Also try adjusting the Irradiance value just above.
Note that Irradiance is also responsible for the amount of FG a shader receives not just emits.
Hope this helps.
Check out this link xsi base. Xsi uses Mental Ray as its standard renderer. Some settings/names may be different but the principles apply to Mental Ray for Maya. See how he uses a MIX of GI and FG to achieve the effects shown down the page.
Also note that in Mental Ray for Maya accuracy for final Gathering is basically No. of Rays. In xsi it is called 'accuracy'.
Mayan elder......only in years.....