Pulse oximeters give biased results for people with darker skin
This really isn't a big deal.  Doctors know that these pulse ox meters aren't very accurate and use them accordingly.  Nobody's changing their plan because you have a pulse ox of 93 instead of 95.  They're there to quickly measure big changes that indicate a problem.  In other words, they're looking for patients going from 98 to 75, not 98 to 95.