The snowflake is a perc (I believe), so the two could even pair up....just make sure the snowflake is smaller than your current clown (or much bigger).
You want to make sure you dont have 2 females in the same tank, as they may fight till the death, although in a 180 I think you would be fine even if they were both female, but if they are both female they can not pair up and will be seperated all the time.
Snowflakes are A. Ocellaris, chances are they can live happy together but won't pair up, but hey never know you might be able to get a new breed going... GL
White and black percs are Ocellaris as well, black and white perc and a false perc (A. Ocellaris) is what makes snowflakes.
Black & White Ocellaris Clownfish
Info from site:
The Black and White Ocellaris Clownfish, also known as the Black Perc, Black Percula Clown Anemonefish, or Black and White False Percula Clown and is normally found in association with anemones on the reefs of the Coral Sea. It can be found individually, or more commonly, in pairs or small groups within the same anemone such as Heteractis magnifica or Stichodactyla mertensii. These tank bred clownfish grow to a maximum size of 3 inches in the aquarium, and may be kept singly or in groups.