I would not change the name of the drink completely, only modify it. Do what a
lot of cooks in america do, use the french term, and call it a pamplemousse
sour. Or call it a Florida sour, or better yet a certain city in Florida known
for their grapefruits. If you are using pink grapefruits you could call it a
ruby sour, or something along those lines. As long as you are using the smae
formula as a sour, base liquor, citrus, and sugar, served on the rocks, then I
think it is not only legitiamte to use the smae name, but less confusing. You
would be letting the guest know that what they are having should be similar to
a sour but with its own nuances, hence the modifiaction.