I just was wondering aloud if Red is the best branding or if — especially now — there might be other benefits to coloring it a different color. For example, as a transit map nerd, I get extra little adrenaline boosts when I look at a map of transport for London and go “ahhh the Croydon Tramlink”, just like seeing the map you shared that has special colors for high frequency bus lines. While not everyone is like that, I do think there is a certain visual impression that seeing “more lines” on a map makes. It visually signals that this is a robust and comprehensive transit system, and for mattapan, could signal that the T has special lines in special urban districts. And it also might reinforce the idea of mattapan and Milton as their own transit district, which expands the viewer’s impression of how big the overall city is (eg, seeing the croydon tramlink way down south of London reinforces just how vast greater London is).For better or worse, the Mattapan Line has been branded as part of the Red Line since the MBTA adopted the Cambridge Seven rebranding in the 1960s. To the T's credit, it's never been shown as contiguous -- there's also been a gap or other visual discontinuity to imply the need to transfer.
I suppose that would come at the expense of visually signaling that if you use the mattapan line, you’re physically connected to the benefits of the Red, and might suggest to many that the service is “inferior”. But since this is a maps thread, and maps are all about what they convey to the reader symbolically, I think this is an interesting concept to think about.