KNOWN ISSUE: Colouring of particle tracks plotted as tubes
If particle tracks are plotted with the Track Type set to 'Tube' and the Colour set to 'Constant', then the tracks are plotted as black rather than the correct colour.
A coding error means that the colour is missing.
Tubes can be coloured by variable, and so colouring with respect to a variable that is constant, and setting an appropriate variable range, can probably get what is required.
ANSYS CFX Release 12.1.