route_color paints the badge and route_text_color writes the route name on
it. When they are the same colour, or close enough, nobody can read the badge.
The spec even says it: the text colour must contrast with the route colour.
The law
A route sets both colours, and the contrast between them is below 1.5:1 (the WCAG minimum for any text is 4.5:1).
How to get pardoned
Pick a text colour that can be read on the route colour. When in doubt, black or white, whichever contrasts more.