Colour-colour and colour-magnitude diagrams. Shown are g − r vs. z − W1 colour-colour diagrams (upper panel) and W2 vs. W1 − W2 colour-magnitude diagrams (bottom panel) for a populations of objects from the spectroscopic data set such as stars (left column), galaxies (middle column) and quasars (right column). The purple contours correspond to the 68th percentile of each Gaussian IGMM component. The green filled circles correspond to the means μ_k of the Gaussian components. The grey scale indicates the abundance of the sources in each diagram.