Colour of carbon particles in geant4

Hello experts, I was simulating the interaction of a carbon beam of energy 20 keV on a Zr target. The beam is in a charge state +1 and I have used GPS to simulate the beam. The major problem I face is while visualising the simulation. As the beam is positively charged, I am expecting the tracks to be in blue colour. But in fact it appears without any colour. This really confuses me. In vis.mac macro, the particle trajectories are explained as follows:
/vis/modeling/trajectories/drawByParticleID-0/set e- red
/vis/modeling/trajectories/drawByParticleID-0/set gamma green
/vis/modeling/trajectories/drawByParticleID-0/set neutron yellow
/vis/modeling/trajectories/drawByParticleID-0/set deuteron pink
/vis/modeling/trajectories/drawByParticleID-0/set alpha blue
/vis/modeling/trajectories/drawByParticleID-0/set GenericIon blue

I am assuming it is the GenericIon is taking care of the colour of tracks of carbon or any other ions (or am I wrong ??). I am attaching the relevant portions of my GPS source macro as well here.

/process/activate msc
/gps/source/intensity 5.

/gps/particle ion
/gps/ion 6 12 1
/gps/pos/type Beam

(the incident surface is in the x-y plane)
/gps/pos/rot1 1 0 0
/gps/pos/rot2 0 1 0

(the beam spot is centered at the origin and is
of 1d gaussian shape with a 1 mm central plateau
Change the beam shape to an ellipse)
/gps/pos/shape Ellipsoid
/gps/pos/centre 0. 0. 30.0 mm
/gps/pos/halfx 6.0 mm
/gps/pos/halfy 3.5 mm

( the beam is travelling along the X_axis with 5 degrees dispersion)
/gps/ang/rot1 1 0 0
/gps/ang/rot2 0 1 0
/gps/ang/type beam1d
/gps/ang/sigma_r 2. deg

( the beam energy is in gaussian profile centered at 2 KeV)
/gps/ene/type Gauss
/gps/ene/mono 20 keV
/gps/ene/sigma 10 eV

I am also attaching the OGL visualisation of the simulation.

I am confused if it is some problem in my visualisation or if it is a problem with me defining the source. Thanks a lot for your help and support in advance.

_Geant4 Version:_geant4-v11.1.2
_Operating System:_Ubuntu 22.04
_Compiler/Version:_gcc 11.4.0
_CMake Version:_3.22.1

1 Like