Accuracy is probably around 9 or 10 for some things (Extended Black is dominant over Partridge, Silver is dominant over gold, percent of offspring with certain gene combinations when crossing certain parents.)
Accuracy is much lower for some kinds of details (picture shows a chicken with Extended Black being black all over, but it can actually have leakage, sometimes lots of leakage. Chicken with Extended Black and I/i+ is shows as white all over, but would often be Paint in reality, because of black leakage.) Maybe 6 or 7 out of 10?
I can't assess accuracy for some other things (pick a color from the list, how many chickens have exactly those genes? There are many colors that can look alike while having very different genes involved. For example, a solid white chicken can be created in quite a few different ways.)
Overall, I don't know how to give a number to the whole thing.