As a formal-Coke-Addict, I have surfing thru the web and found that ....
Coke Zero release to US market on 2005 June (Announced on 2005 March)
US version use white color for can and claims it is zero in calorie
I got my white can (parallel import) from CitySuper on 2006
It also seen that White can version claim it is zero in Calorie
But Black can version claim it is zero sugar (in Hong Kong, at least)
That's means it may not zero in calorie
It seen to me different countries have its own can design and formula in making Coke Zero
However
Japan Coca Cola haven't call it ZERO, it just called "No Calorie Coca Cola"
And Japanese use Sliver color as packing

This is the original white can, from
MSNBC on-line news (2005)

This is image capture frorm Coke Zero promotion website, show here the white color can and traditional red Coke

Black Can(s) from other website all over the world ...
All claim only "zero" sugar, not calorie



Official Coke Zero web-sites
United StatesGerman