Color Specific inventory list
Also keep in mind that color will change on some parts as they age (depending on environmental factors). New or less exposed parts in the "old grey" can be a different shade than original, aged parts in the same "old grey".  The blue-grey parts that you have might actually be categorized as a blue instead.

Check out how lego sells the colors today, here:
http://shop.lego.com/en-US/Pick-A-Brick-11998

The peeron color table is here:
http://www.peeron.com/inv/colortable/3020

Check out your set here as well:
http://www.brickset.com/detail/?Set=7150-1

The colors in the grey family (or sometimes confused as grey) are referred to as on brick set (on peeron if different):
Black
Dark Grey (OldDkGray)
Dark Stone Grey (DkStone)
Grey (OldGray)
Medium Stone Grey (Stone)
Sand Blue

Your set has "Grey" and "Black" from this list.  If you ordered new parts from Lego, the lighter shade of grey would be "Medium Stone Grey" form this list.