Hence the Ravenswood, today's Brown Line, was named for the street and neighborhood it went through for a portion of its route. The Douglas Park (Pink Line), and the now defunct Humboldt and Garfield Park Lines, merely ran in the vicinity of those west side parks. The term Lake Street L, a portion of today's Green Line, was much more descriptive as the entire route ran above its eponymous street, until it circled around the Loop and returned back to its origin at Harlem Avenue. The Howard Line, now the Red Line, and Jackson Park and Englewood Lines, two branches of today's Green Line, actually terminated at the places for which they were named. Old habits die hard and today you still hear old timers, myself included, using those old terms, causing much confusion among the newbies.
Today of course all the lines are color coded, inspired by the MTA in Boston. Unlike Boston, the CTA's cars are not painted in the colors of the line as the cars are called into service on multiple lines. The new LED displays on the 5000 Series cars seem to have done away with any color reference whatsoever, making the point of naming lines after colors somewhat moot. Like most of the subway systems in cities around the world, the trains display their final destination stops, making the CTA more understandable to riders from out of town, at least those who are familiar with any of those other systems.
Perhaps the most confusing aspect of the old L system was the use of alternating rush hour stops. During peak periods, trains would run alternately as either A or B trains, and stations would alternate between being either A or B stations. The more heavily used stations would be designated AB stations. The trains would only stop at the stations with the correct letter, meaning for example that if you needed to get on at an A station and off at a B station, you would need to take an A train to an AB station and transfer to a B train, which sometimes involved back-tracking. This made for quite interesting conversations between novice riders and more experienced ones.
All this was done away with when the L became multi-colored.
I kind of miss it.