There is a common misconception that 'farang' is just a general term for foreigner. In fact, it specifically refers to people from a western ancestry (Americas, Europe and Australasia). Thais do sometimes umbrella black and asian people from western countries under the farang label but generally the word is specifically used for white skinned people. Black people may be called farang dum (black farang).
We hear the word farang so often that it is easy to assume they are always talking about us. The word is used in other contexts. It is also the Thai word for the guava fruit. mahk farang is the Thai word for chewing gum. man farang is the Thai word for potato. Note they are all items that were introduced to Thailand from the west.