RGB colour–composite image of the optical counterpart of cluster PLCK G100.2-30.4, as obtained with the IAC80 telescope. R, G, B colours are g,r and i-band Sloan filters, respectively. Although the IAC80 field of view is 7′, this image is trimmed to 4.8′ × 2.7′, and is centred at the XMM-Newton counterpart (white iso-contours). Red galaxies defining the red-sequence of the cluster are clearly seen at the centre of the image.