  Recent TESS-based studies have suggested that the dayside of KELT-1b, a
strongly-irradiated brown dwarf, is significantly brighter in visible light
than what would be expected based on Spitzer observations in infrared. We
observe eight eclipses of KELT-1b with CHEOPS (CHaracterising ExOPlanet
Satellite) to measure its dayside brightness temperature in the bluest passband
observed so far, and model the CHEOPS photometry jointly with the existing
optical and NIR photometry from TESS, LBT, CFHT, and Spitzer. Our modelling
leads to a self-consistent dayside spectrum for KELT-1b covering the CHEOPS,
TESS, H , Ks, and Spitzer IRAC 3.6 and 4.5 ${\mu}$m bands, where our TESS, H ,
Ks, and Spitzer band estimates largely agree with the previous studies, but we
discover a strong discrepancy between the CHEOPS and TESS bands. The CHEOPS
observations yield a higher photometric precision than the TESS observations,
but do not show a significant eclipse signal, while a deep eclipse is detected
in the TESS band. The derived TESS geometric albedo of $0.36^{+0.12}_{-0.13}$
is difficult to reconcile with a CHEOPS geometric albedo that is consistent
with zero because the two passbands have considerable overlap. Variability in
cloud cover caused by the transport of transient nightside clouds to the
dayside could provide an explanation for reconciling the TESS and CHEOPS
geometric albedos, but this hypothesis needs to be tested by future
observations.
