The locator bar shows every tracked player as a colored marker, and /waypoint modify is how you control that marker. Pick one of the sixteen named colors, set an exact hex value when the palette is not enough, change the marker style, or reset back to default — the generator writes the modify form current versions accept.
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The locator bar shows tracked players as coloured markers along the top of the screen. /waypoint modify sets a player marker to one of the sixteen named colours, an exact hex value, or a custom style, or resets it to default.
Use the hex option instead of a named colour. /waypoint modify <target> color hex <RRGGBB> tints the marker to any colour, which the sixteen presets cannot cover.
The locator bar and /waypoint are recent additions, so older versions do not have the command at all, and the bar must be enabled for markers to appear. Select a current version in the edition and version control next to the module list for valid output.