Unlike other people I find the portraits surprisingly diverse, I expected to see very white faces considering most "realistic" representations are from white actors and white statues erase features. Not a perfect project but interesting.
Roman emperors came from all over the empire, so the diversity is to be expected (e.g. Heliogabalus was from modern Syria, and there's noticeably Philip the Arab)
What is odd here is that it's actually likely overdone, as the "blondies" in roman times were unusual enough that they were explicitly noted as such, e.g. Lucius Cornelius Sulla Felix was noted as "his golden head of hair gave him a singular appearance".
We have plenty of colored images from roman times through mosaics.
It's worth noting that classical statuary was typically painted and not left as blank white marble (the practice has persisted in some Catholic statuary). I doubt that any remaining pigment on statues (which might be recoverable through microscopy) was incorporated into the models for creating these images, but it would have been cool had it been.
It would be interesting to compare the colourisations to where any of the emperors are known to have originated and whether they came from Northern or Southern Italian ancestry. A blued-eyed blonde from Northern Italy would be quite feasible.
