Correct diameter and name for wire for LED cathode connection
If 0.8 is the diameter (in mm) for the red single-conductor, that corresponds to 20AWG wire, which seems appropriate for the use in question.  So what you want to search for is 20AWG Single-Conductor Wire in your color of choice (unlikely to come in a metallic silver, but possibly in gray and most definitely in white).  From electronics distributors like DigiKey and Newark, it's labeled as "hook-up wire".