you should try going into the keying parameters and tweaking the color replacement curves
actually there is a color picker to let you choose the color you want to shift
after selecting the color, a red bar appears in the color range (the one that has the curves on) you then have to lower the part of the curve that crosses the red bar (not too much) and don't hesitate to add some points (two is good), you'll get much control...
hope this helped
and sorry for my english too
wala wala