Very frequent, actually I know many who are much lighter than I am.There are certain individuals in an ethnicity who can't pass at all as their own ethnicity. For the most part, majority of people can still pass as their own ethnicity to varying degrees. Take a look at Tiglat for example AKA GREAT SARGON. He claims to be 7/8 Kurdish but he can't pass as Kurdish. On the other hand there's me who is 3/4 Georgian Jew and I don't pass as a typical Georgian Jew, however I can still somewhat pass.
How frequently found is your looks in Assyrians?