Trouble with "Pick Up Underlying Color"?

[zookman]

I was checking out the latest Painter video tutorials on www.lynda.com and ran through a lesson entitled "painting with pick up underlying color". In it, they demonstrate this Layers palette feature:
1) Created a new default layer and added a patch of red to it with the Acrylics brush, Captured Bristle variant.
2) Created another default layer (on top of the previous one) and added a patch of yellow to it using the same brush. This was painted directly over the red patch. The yellow was completely opaque.

That's because, as the instructor pointed out, the "Pick Up Underlying Color" checkbox was *not* checked. She then turned on Pick Up Underlying Color and applied more yellow paint. This time, the yellow blended with the underlying red, producing a kind of orange. Very cool.

The problem is: when I tried to duplicate this very simple task, I could never get the top layer to blend with the layer underneath, as if the Pick Up etc. option was never checked. Am I missing something?

For the record, I *am* using IX.5 on a Windows XP Pro platform with gobs of RAM memory.