Pop your hood and look at the white sticker containing all the cars info from the factory. There is a line item for paint / interior colors and beside it lies the code.
They goofed and did not spray your bumper with the correct artic silver variant. Alot of Porsche colors have multiple codes...Don't have a clue why, because it can cause exactly what you just went through...
Just take it back to the company and if they are a reputable business, they should take care of the problem. If they specialize in P cars, they will know what's up.
See this link...
http://www.piperboxster.com/paintcode.htm