There is a certain tendency to think that ones appearance and the appearance of ones siblings are quite different, while, quite often, non-family members experience them as very similar. From a European perspective "all Chinese look alike"; and it has also been said, that, from a Chinese perspective, "all Europeans look alike".
So it seems as if there are two cognitive tendencies/biases: (A) the tendency to perceive more similarity than there actually is (B) the tendency to perceive less similarity than there actually is.
Or in other words: (A) the tendency to perceive the similarities and to ignore the differences (B) the tendency to perceive the differences and to ignore the similarities.
Bluntly said, in some situations people appear to be blind to equality, while in other situations people appear to be blind to inequality.