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The colour coordinates on standard CIE 1931 chromaticity diagrams are presented for NCS (15 soda-15 lime-70 silica (mol%)) glasses, singly and doubly doped with the transition metals (Ti, V, Cr, Mn, Fe, Co, Ni and Cu) at low concentrations (≤1 mol%) and with various rare earth dopants (Ce, Pr, Nd, Sm, Eu, Tb, Dy, Er, Ho). The colour coordinates were calculated from the transmission spectra in turn determined from measured glass absorption spectra. The colour coordinates of 232 glasses are reported, showing which colours can be made with common colouring dopants, and how their coordinates depend on: dopants, concentrations, sample thickness, melting conditions (oxidising electric furnace and reducing gas furnace) and concentrations of agents added to the batch as oxidising (NaNO₃), reducing (C) and/or refining (Na₂SO₄) agents. Cu shows the greatest variability. The varying oxidation states of the dopants and their coordination are the main reasons for colour differences. The effect of the glass thickness in the colour appears because the absorption peaks can be very high and locate partly outside of the visible light range that changes the proportions of the spectrum that stimulate the three colour receptors in the eye.