Jeff,

In picture three the apple is red to start with (as can be seen in the layer history) but turns "silver" when the monochrome box is checked in the channel mixer.  When this box is checked the output channel field should show "gray" (top of the channel mixer window).  There should be no b/w effect at all on the car picture if the clipping mask has been applied to the apple layer.  Also the apple shouldn't change back to red whilst the monochrome box is checked and the output channel field displays gray.  If you uncheck the monochrome box the apple still stays silver but RGB values can be reintroduced bringing flat colour back to the apple.  With the apple image in grayscale the overlay blending mode turns the white areas transparent.  Using the channel mixer sliders simply adjusts the balance of the gray scale transitions.

If you are still having problems upload your source pictures and I'll have a look or a screen shot showing your layer history.

Shane.

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