  Colour-magnitude diagrams form a traditional way of presenting luminous
objects in the Universe and compare them to each others. Here, we estimate the
photometric distance of 44 transiting exoplanetary systems. Parallaxes for
seven systems confirm our methodology. Combining those measurements with fluxes
obtained while planets were occulted by their host stars, we compose
colour-magnitude diagrams in the near and mid-infrared. When possible, planets
are plotted alongside very low-mass stars and field brown dwarfs, who often
share similar sizes and equilibrium temperatures. They offer a natural,
empirical, comparison sample. We also include directly imaged exoplanets and
the expected loci of pure blackbodies.
  Irradiated planets do not match blackbodies; their emission spectra are not
featureless. For a given luminosity, hot Jupiters' daysides show a larger
variety in colour than brown dwarfs do and display an increasing diversity in
colour with decreasing intrinsic luminosity. The presence of an extra absorbent
within the 4.5 $\mu$m band would reconcile outlying hot Jupiters with
ultra-cool dwarfs' atmospheres. Measuring the emission of gas giants cooler
than 1000 K would disentangle whether planets' atmospheres behave more
similarly to brown dwarfs' atmospheres than to blackbodies, whether they are
akin to the young directly imaged planets, or if irradiated gas giants form
their own sequence.
