The reason the button is red is because it hasn't calculated the path there yet.
If you leave the galactic map and come back to it you'll see it may well have calculated it but anything above 45 ly can take forever. The reason why is that to plot the paths each 10 LY adds more and more paths increasing the plotting requirement excessively for whatever algorithm they are using. Also I would imagine the procedural nature of the galaxy adds to this calculation time. As someone said above this algorithm really needs updating.
It needs to be put client-side. I don't care if that algorithm was written by rube Goldberg a single core on my processor could plot all conceivable routes within 5,000ly in an inconceivably small amount of time. Naturally the route calculations are set as a very low priority on the servers to prevent stability issues.