[CobaltBlue]

My older son did an experiment for science fair that seemed to prove that dogs can distinguish yellow and blue. Unfortunately, it was disqualified because of rules about "experimenting on animals" - in this case, feeding our Golden Retriever, Lizzie, morsels of dog kibble on various colored paper plates. And now he's lost interest, so it remains for later generations of science to research.

[krb]

Yellow and blue have different values (intensities) as well as hues (color shade).

If you really want to see if dogs can distinguish color, you need to select two different hues with the same intensity (i.e. they would appear as the same shade of gray if photographed in B&W).