Tekkonkinkreet which be a 2006 Japanese anime based on Taiyo Matsumoto's Manga series from the 1990s.
It's the story of two orphan streetkids "Kuro" (Black) and "Shiro" (White). Kuro is an angry streetwise kid and Shiro is a dreaming innocent. Black and White, see? Anyway this is their story of survival in the gritty corrupt streets of Treasure Town with its cops and Yakuza.
I do love the little film so much... the dark gritty streetlife, the fantasy, the art work.... I do get myself a copy on DVD straight away.