merge_colour, with the UK spelling, doesn't work while using live, it just returns 0 instead of the merged colour.
merge_color, with the US spelling, does work correctly.
To reproduce in a new project with GMLive.gml, add the following to obj_gmlive Draw:
var _col1 = c_fuchsia; var _col2 = c_aqua; var _blend = (sin(current_time / 1000) * 0.5) + 0.5; draw_text(0, 0, string(merge_color(_col1, _col2, _blend))); draw_text(0, 20, string(merge_colour(_col1, _col2, _blend)));
Running the project with live enabled, we see merge_color works, and merge_colour works for a hot second but then starts returning 0 after "Ready!" pops up in output console.