  We present the rest-frame colour-magnitude diagram for 35 early-type galaxies
in the Hubble Deep Field with median redshift 0.9. Although with considerable
scatter, a red sequence well-described by the passive evolution of an
intrinsically old stellar population is observed. Comparison with the passively
evolved colour-magnitude relation of the rich Coma cluster ($z=0.023$)
indicates that around half of the early-type galaxies in the field at this
redshift are as old as those in rich clusters.
