rekordbox and nxs2 players allow the DJ to assign a color to a hot cue, and use more than three hot cues in a track. These features are supported in the .EXT file with a PCO2 tag.
The following commit shows the current state of the areas in Crate Digger’s Kaitai Struct file that parse this information, in case you want to add it to python-prodj-link: Deep-Symmetry/crate-digger@9589538
And this shows the translation between rekordbox color codes and actual displayed colors: https://github.com/Deep-Symmetry/beat-link/blob/10fada15abca4b41ab2435734961b10d95413abd/src/main/java/org/deepsymmetry/beatlink/data/CueList.java#L453-L505