User reported issue: increase graph trace contrast

This was reported into phethelp by a Linux user and was likely caused by a graphics issue on their machine. However, I thought it would be best to get it recorded so that if/when this sim is revisited we could investigate increasing the contrast or modifying the colors of the probes/traces.

I see the dark trace, but the "light trace" is invisible, as is the grid that underlies the traces. The only evidence of the light trace on my computer is that in the places where it crosses the dark trace the dark trace has a small "gap" like you erased it with a pencil. My first thought in running the sim was that the light trace did not exist, I only noticed it did exist when I wanted to report the error and brought up the "report a problem" box. This seems to have changed the look-up table on my display so that the light trace became visible.

It is possible that your color scheme is just a little bit too subtle. Maybe your dark trace should be black 100% (I am guessing it's black 60% or so now) while your light should be black 40% (I am guessing it's black 10 or 20% now). Or let them be blue and red or something ...

No source file, test, or code entry point is identified. Start by reproducing the wave-interference trace and grid visibility problem on Linux; done means both traces and the underlying grid are clearly visible without relying on the report dialog.