Human emotion has faded because the world's government has decided that a docile population is a safe and prosperous population.
There aren't' colours anymore and everything is a shade of grey, drugs hidden in people's food stifle creativity and strong emotional response. Music is Dead and Books and TV exist only to inform.
But a rebel group exists who have worked out a way to bring colour back into the world with paint that counter-acts the drugs in people's systems - Specific emotions keyed into specific colours that physical contact or prolongued nearby exposure to causes the chemicals supressing those emotions to be eliminated from the body.
Heavy themes of Liberty, Disregard for Authority and Beneficial Rebellion.
Somewhere between very, very dark but relatively non violent. For the most part, combat would focus on... well, paint. The police have high quality gear and grey paint that basically acts like riot foam whilst the players have acsess to a ton of colours.
Jet Set Radio crossed with 1984 I guess, with some Splatoon thrown in there for good measure