I've noticed a few conflicting paint code numbers for Sonic Blue. It seems that the SVT has a specific paint code of S1, while all other cars have SN. I'm not sure if there really is a difference between the two paint colors. In any case, your best bet will be to go to the local paint shop anyway.
Mine: 2004 Subaru WRX Wagon: 116k, WRB
Gone: 2002 SVT, #1654
Hers: 2012 Focus Ti Sedan: 67k, SGM, Manual