You could also get factory colors “custom”. What was available at the dealership was one thing, but they had a host of other color options you could special order. Like upgrading from an AM radio to AM/FM Cassette. You just had to wait for the factory to do a run of that option before your car would get shipped. More options were a la carte and you weren’t forced into trim packages like today that are like cable tv packages - pay for a bunch of shit you don’t want to get the one or two options you do. Want AWD? Sure! But you have to take “premium sound”, floor mats, cargo separator, and exterior trim packages too.

Some still have a bunch of color options. Hell, look at all the colors you can get through BMW Individual for example.

But people are scared about resale values and stuff

For regular makes and models there are far fewer options, like Toyota or Honda. BMWs are perceived as higher tier and have more options. The fact you have to single out a more luxury brand and can‘t just say “Toyota has 20 color options for the Corolla!” proves my point.