Ramin Djawadi has created a new theme for Ramsay, which sounds quite fitting for how deranged he is. It first played when he stabbed Roose, and it played last night when he murdered Osha and when Jon read out the Pink Letter.

EDIT: Another observation on the score. A prolonged rendition of 'Chaos is a Ladder' plays when Littlefinger manipulates Sweetrobin and Yohn Royce into providing him with the Vale's army. Previously, it had appeared in season 5 when Littlefinger was in the carriage with Sansa, and also when Cersei had ordered Mace to go to Braavos. As others have noted in other threads, prior to its usage as LF's theme, it was the seemingly the original leitmoff for House Lannister, and I think that this cements that it is indeed his own theme.