  Galaxy colours are determined for two samples of 6C and 3CR radio sources at
z~1, differing by a factor of ~6 in radio power. Corrections are made for
emission line contamination and the presence of any nuclear point source, and
the data analysed as a function of both redshift and the radio source
properties. The galaxy colours are remarkably similar for the two populations,
and the UV excess evolves with radio source size similarly in both samples,
depsite the fact that the alignment effect is more extensive for the more
powerful 3CR radio galaxies. These results seem to suggest that the alignment
effect at these redshifts does not scale strongly with radio power, and is
instead more closely dependent on galaxy mass (which is statistically
comparable for the two samples). However, it is likely that the presence of
relatively young (< several 10^8 years old) stellar populations has
considerably contaminated the K-band flux of these systems, particularly in the
case of the more powerful 3CR sources, which are ~0.5mag more luminous than the
predictions of passive evolution models at z~1. The higher luminosity of the
3CR alignment effect is balanced by emission at longer wavelengths, thereby
leading to comparable colours for the two samples.
