Color Their World

A while back, talking about one of Buster's misadventures, I said something about a dog treat being similar in color to my skin. Now, though, I'm wondering about that.

The set of all colors - all wavelengths of light in the visible spectrum - is infinite-dimensional. The colors we (most of us) are able to perceive make up a three-dimensional projection of that set - three, because of the three types of cone cells in our eyes.

It has recently been verified that dogs are dichromats, with two types of cone cells, and hence they perceive a two-dimensional projection. If that projection is itself, more or less, a projection of ours, then colors that look alike to us will also look alike to them; but if not, then not. This would, I suppose, depend on the frequencies which cone cells are most responsive to; if canine cone cells peak at or near the peak frequencies of two of our cone types, then they can't distinguish what we can't distinguish.

Does anyone know whether this is true? The Wikipedia article simply says that most non-primate mammals are red-green color-blind, but it's not obvious to me that resolves my question.

Inconsistent (But Sticky)

Today, ye olde procrastinator got around to some recycling. I had several empty peanut butter jars, and I put them through the usual routine: a soak in soapy water, a couple of rinses with hot water, some action with a Dobie to get the more recalcitrant bits, and one last rinse. This time, it occurred to me to check the lids: they are a different plastic, but are they recyclable? I looked for the triangular symbol, and found it - on two of the four lids. Apparently some are, and some aren't. It strikes me as odd; they were four jars of the same size and same product (40 oz Jif Extra Crunchy), all purchased at the same store, although, admittedly, over a period of two or three months. I don't know whether the ones with recyclable lids were bought earlier than, later than, or mixed among those without.

Is a puzzlement. I guess in future I'll have to check the lids individually.