difference between grinding stone colours

[gttjames]

guys which one of these grinding stones should i be using 1st to take off most metal, then 2nd, then 3rd ???

http://www.ebay.co.uk/itm/1-4-ROTARY-STONE-FILES-DRILL-DIE-GRINDER-GRINDING-BITS-/120869190210?pt=UK_Home_Garden_PowerTools_SM&hash=item1c245d7a42

[Bigfoot]

Would say grey, then pink then white