Grey caulking on teak decking

[BartW]

Actually, I struggle to think of one single aspect where teak is superior to non-skid GRP,

P, that is the same question like asking " I struggle to find one good reason to own a boat"
for me, (real) teak is just part of the complete boating experience

to OP:
for a new boat, my choice would be grey caulking.
for my old lady, I stick with black. even on the new teak to be placed hopefully coming winter