Conversation so far:
What was The Kinks's musical style?
popular R&B and blues styles; then, under the influence of The Kingsmen's "Louie Louie" recording, developed louder rock and hard rock sounds.
What was their favorite style to perform?
Dave Davies was "really bored with this guitar sound - or lack of an interesting sound" so he purchased "a little green amplifier ...

Question: What did the green amplifier do?
Self-contained rewrite: What did the green amplifier do to Dave Davies' guitar sound ?