Master palette - Doppio?

They're both correct, with the adjective respecting the gender of the noun:
doppiO segnO and doppiA codA

Double chocolate chip cookie with coffee:
Ricetta Biscotti al doppio cioccolato e caffè

Double cream:
Doppia crema

but...
Double trouble:
Doppio problema

Most Romance languages have nouns with gender and adjectives must match the gender of the noun. So, presumably it's Doppia Coda and Doppio Segno.

Any actual Italian speakers to confirm? (I only have Spanish and French :-)