All spectroscopically confirmed stars (green), QSOs (red) and galaxies (blue) from SDSS plotted in variability fit parameters (top) and colours: g – r vs. z – W1 (middle) and W2 vs. W1 – W2 (bottom). Marker colours show the object class and blend to grey or black when multiple classes occupy the same parameter region. A heat map of all spectroscopically confirmed objects is found in Fig. B.2 for comparison with Fig. 1.