The slits themselves have colour. Each colour bends by its own wavelength — so the light fans into the rainbow.
R G B slits: three colours through the same slits — blue diffracts tight, red diffracts wide, so their fringes separate. Rainbow slits: the full spectrum — a bright white centre where every colour agrees, fringes fanning into rainbow and washing out (Asolaria as the white-light photon). 3 rainbow spheres: the same light caught on three translucent convex spheres with rainbow cells — the pattern wraps the curve instead of a flat wall.