While adjectives generally follow the noun in Irish the opposite is the case for compound nouns created by a noun and adjective.

Dubh: black

Na Dubhaoiseanna = the Dark Ages

Dubhoighear = Black frost

There are also many words in the dictionary beginning with 'du' which derive from 'dubh'

Therefore, Dubhlinn (Dublin) = Black Pool. There is nothing strange about that construction. It is quite logical to assume that was the original name which was 'norsified' by the Vikings.

Even though 'bh' is usually pronounce roughly as 'v' in modern Irish it was probably pronounced as 'b' in earlier times.

Regarding the prefix 'baile' so common in Irish placenames; it very often equates to 'townland' the smallest unit of territory found on Irish maps.