The Skillcape Customiser is an interface unique to the max cape and completionist cape that allows the wearer to choose the particular colours of the cape. Herald capes, clan cloaks, the RuneFest 2011 Hood, and the RuneFest 2013 Cape can also use a similar customiser, however they do not have the right click "Set H/S/L" and "Get H/S/L" options that the max and completionist capes have.
There are four different areas on both capes that may be recoloured, defaulting to a red theme. The colour scheme is shared between an account's max and completionist capes, so they cannot have different themes. Clicking the reset button on the bottom right part of the window will reset the cape to the default colours.
The colours on the cape are represented with hue-saturation-lightness coordinates. Unlike normal HSL coordinates which are in the ranges [0,360°) for hue, and [0,100%] for both saturation and value, the system RuneScape uses the ranges [0,63] for hue, [0,7] for saturation, and [0,127] for lightness. This allows for 65,536 uniquely defined colours.
Hue determines what part of the spectrum will define the integrity of the colour. Starting with low values, the spectrum follows the colours of the rainbow: red, orange, yellow, green, blue, purple, and rolling over back to red. The range for hue is 0 to 63, inclusive.
Saturation determines how intense the colour will be. Lower values produce grey, and higher values produce "purer" colours. The range for saturation is 0 to 7, inclusive.
Lightness determines how dark the colour will be. Lower values produce darker colours, and higher values produce lighter colours. The range for lightness is 0 to 127, inclusive.