This was the official artwork that was leaked by GameFreak, right? From this thread: GF Leak Discussion Thread.
Since it’s copyright date is ©2006, it might have been another color in the past. Still, I would personally say ‘pantone 564 coated’ (aka hex code #86C8BC) would be the correct semi-official answer. As for a more human-friendly name for this color, it seems to be close to ‘pearl aqua’ or ‘tranquil teal’. 
Greetz,
Quuador