White cables are invisible on cable trace

[Epaphus]

Environment

• Python version: 3.6.8
• NetBox version: 2.10.3

Steps to Reproduce

1. Have a cable with the colour white
2. View trace of cable

Expected Behavior

A border or similar around the cable to make it clearer it was a white cable rather than no cable.

Observed Behavior

Cable connection within a cable trace is invisible when compared with other coloured cable due to a white cable on a white background

[cpmills1975]

I've raised a PR for this - hope this is acceptable?