  We describe the effect of AGN light on host galaxy optical and UV-optical
colours, as determined from X-ray-selected AGN host galaxies at z~1, and
compare the AGN host galaxy colours to those of a control sample matched to the
AGN sample in both redshift and stellar mass. We identify as X-ray-selected
AGNs 8.7 +4/-3 per cent of the red-sequence control galaxies, 9.8 +/-3 per cent
of the blue-cloud control galaxies, and 14.7 +4/-3 per cent of the green-valley
control galaxies. The nuclear colours of AGN hosts are generally bluer than
their outer colours, while the control galaxies exhibit redder nuclei. AGNs in
blue-cloud host galaxies experience less X-ray obscuration, while AGNs in
red-sequence hosts have more, which is the reverse of what is expected from
general considerations of the interstellar medium. Outer and integrated colours
of AGN hosts generally agree with the control galaxies, regardless of X-ray
obscuration, but the nuclear colours of unobscured AGNs are typically much
bluer, especially for X-ray luminous objects. Visible point sources are seen in
many of these, indicating that the nuclear colours have been contaminated by
AGN light and that obscuration of the X-ray radiation and visible light are
therefore highly correlated. Red AGN hosts are typically slightly bluer than
red-sequence control galaxies, which suggests that their stellar populations
are slightly younger. We compare these colour data to current models of AGN
formation. The unexpected trend of less X-ray obscuration in blue-cloud
galaxies and more in red-sequence galaxies is problematic for all AGN feedback
models, in which gas and dust is thought to be removed as star formation shuts
down. [See paper for full abstract.]
