I have ordered DPD powder for my PS233 kit from Ben for about 5 years now. Last year I did a comparison. I tested the new and old powder side by side. New powder was white and the old powder was darker, had some clumps in it, but it was not black. I crushed the clumps with the spoon.

Both measured exactly the same. That was my experience. I did not keep checking the powders until they did not measure the same. I do know that the darker powder still did its job, but at some point I am sure there would be a difference. Time wise, the darker powder I check was 14 months old, kept inside, and was never wet.

Hope this helps.

Harry