Simultaneous k-means clustering for the chromospheric Mg II h, Ca II H, and Ca II 8542 Å spectral lines. The clusters, labelled in bold, are ranked from most common in the top to least common in the bottom. The fraction of profiles in each cluster is labelled in the top right of each panel. The spectra are interpolated to a constant velocity separation for Doppler velocity between between ±30 km s⁻¹. Clusters of interest are divided into two classes: blue grains, plotted with blue; and red grains, plotted with red. In the figure, all clusters are normalised separately, but the scaling between the three lines in each cluster is preserved.