It’s commonly known that the accuracy of wrist-based heart rate monitors varies greatly among individuals. Factors such as skin thickness, hair, density of blood vessels/capillaries, and skin tone are well-documented. In fact, Valencell, one of the largest producers of optical heart rate sensors for wearable devices, clearly outlines these issues in a 2015 post on this very subject. To what degree that accuracy is degraded specifically for people of color, at this point, is anecdotal at best. As the article also states, the technology is changing rapidly, making thorough studies on this issue even more difficult.
From a exercise and endurance sports standpoint, I think this definitely falls in the category of “old news”. As athletes, we’re much more aware of discrepancies between our device’s data and our perceived effort. Practically all runners have been affected by “cadence lock” while cyclists, due to the gripping of the handlebars, consistently experience poor results. Both groups typically resort to using electrical-based chest straps or arm-based optical devices when heart rate accuracy matters.
It’s the casual user of these devices that is more likely to be affected by these potential inaccuracies as they’re going to assume that an expensive, state-of-the-art, device should be able to perform one of its basic functions accurately and reliably. But based on the size of the market and the sales at stake for companies such as Fitbit and Garmin, it’s reasonable to assume we’ll see rapid and continuing improvement.