In principle, the structure of the RAL DESIGN SYSTEM plus follows the CIE Lab colour space, according to which all the shades are sorted according to hue, lightness and chroma and arranged in a logical mathematical way.
Building on this, the first set of three letters in the RAL DESIGN SYSTEM plus corresponds to the hue H, the first pair to the lightness L and the second pair to the chroma C. This means that for example the shade RAL 270 30 20 is a dark blue with the hue H = 270, the lightness L = 30 and the chroma C = 20.
When using achromatic grey shades, particular attention needs to be paid to ensure that the latter have the hue H = 0. Nevertheless, it is vital that the shade designation shows the first three digits of 000 because otherwise it is easy to confuse it with a shade in the RAL CLASSIC colour collection. Therefore, for example the shade 000 50 00 from the RAL DESIGN SYSTEM plus is a grey shade (hue H = 0 and chroma C = 0), while the shade RAL 5000 from the RAL CLASSIC colour collection is an intense blue shade.