K − L′ color (left) and K − L′ color excess (right) for the ONC binaries. The T Tauri type of each binary is named from the type of each component with C or W (CTTS or WTTS) indicating the presence or not of an inner disk. The dotted lines delimit the regions indicating the presence or not of an inner disk around each component, i.e. WW, CW, CC, and WC, with the first letter referring to the primary and the second to the secondary. Filled square symbols show systems with significant (>3σ) K-band excess r_K which are all found in the primary only. Systems classified as Class II from Spitzer IRAC colors are plotted with large open diamonds.