Throughput of filters NBC iv (dashed line), R_c, i′ and z′ (dotted lines) on Suprime-Cam. An LBG template with EW(Lyα) = 10 Å at z = 5.72 is shown in red. The rest-frame wavelength of the Lyman limit and Lyman α is indicated. For z > 5.7, the ‘break’ at Lyα enters the z′ band and can result in a rapid evolution in the (i′ − z′) colour.