I ordered the invitation paper and the envelopes from Action Envelope. The colors are great - exactly what I wanted:
Aquamarine Metallic for the envelopes and the printed portion of the invitation and Lagoon Metallic for the accent color. They have a little sparkle, but not a lot. The other materials necessary for my DIY invitations - like tiny little starfish - have already arrived. 
I’m going to assemble and test mail myself an invitation from Ocean City this weekend so I can make sure they hold up well in the shipping.