Your interior is actually dark charcoal as kornnut said, and actually the seats you posted:
are the same as these:
As I've said from the beginning, the only way you're going to get "silver" seats is if you buy custom seats or buy new leather from a company like katzskins how hard is it? Your only other option is to try and find the '99 anniversary seats but good luck with that. It's unlikely you'll ever find them and if you do get ready to spend big money on them.
That color shown in those pics is medium parchment. The dark charcol seats would look the best IMO for your car. My buddy had a convertible like yours and I couldn't figure out for the life of me why they put white leather seats in a yellow car with dark charcol interior. Oh well Its your car do what is gonna make you happy.