So, I set myself up with 8.02% hit (263 rating) tonight and afk'ed behind a target dummy for 1600 swings. Out of these, I found 0 misses, 76 dodges, 100 crits, 400 glancings, and 1024 normal hits.
With 8.02% hit and a 9% base miss chance, the odds of me seeing 0 misses in a sample size of 1600 is: (0.9902^1600) = 1.4344e-7, or 0.0000143%. Seems pretty obvious that the miss chance is no longer 9%.
If we do the same math assuming different base miss rates:
Miss ErrorProb Odds that the base miss chance is lower than this
9.00% 1.4344e-7 99.999985%
8.50% 4.535e-4 99.954%
8.25% 0.02511 97.489%
8.10% 0.27789 72.21%
Screenshot
I also have 400 devastates logged without a miss, giving a confidence of 98.05% for the 9% miss scenario. It's not nearly enough to confirm that yellow misses are below 8.5%, but it is almost certainly not 9% anymore.
Edit: Swung a few more times, up to 2751, still no misses. Unless raid bosses are different than the heroic training dummy (which may be the case), the white hit cap is almost certainly no more than 8.02%.