I snapped this pic about 15 years ago. It provides an example of some of the color shades found in the Cochrane Bells: near-clear straw with the slightest of a pink tint; light pink; and medium purple. I had acquired well over a dozen sets from one source, as well as many single bells and hardware. There were a few single bells that were heavily damaged, so they made it into our cactus garden. One piece was the lighter straw/pink tint shade. Now, 15 years later, after spending the same number of years fully exposed to the sun, it remains the same. All the sets appeared to have seen years of exposure, so it is my belief that the lighter shades are stable and will not turn any darker. You can reference another pic here that I posted a couple of years after this same group was acquired: [id=194011387]

I will add, though, that the purple examples were likely clear at the point of manufacture, so any clear sets out there that have not seen exposure could very well turn purple if exposed to sunlight.