It has always been that way in GA. The only GA Governor from Atlanta, oddly enough, was Lester Maddox.
What GA is becoming is more black. GA now has the 2nd highest black percentage of the population of any state, with MD the third blackest (a bit of a surprise). MS is tops, but the surprise is that SC and AL are behind GA. Of course, most of this black growth is in metro Atlanta. Check out the increase in the population in general, and in the percentage of the black population in Gwinnett and Cobb Counties, counties that were once the most Republican counties in GA at the Presidential level.
Also whites in the Atlanta area are slightly more willing to vote for Democrats than other Southern states. From 2010 census data you can actually a draw a clean majority white district centered in North DeKalb County, North-Central Fulton County, and Western Gwinnett County.
