Saw this first on Curbed SF — Google maps now displays color-coded BART lines, along with the Caltrain line. Apparently the San Francisco Bay Area is the first metropolitan region to get this feature. Click the thumbnail to go to Google maps and see the BART and Caltrain lines (the latter being the grey line going down the Peninsula, of course).

However, the feature only displays a straight-line route map from station to station, often distorting the actual location of the route taken between stations.

Click the image to see it on Google maps.