A lot of the newer cars have a black trim around the windows. Generally this has to be painted on. This hardly turns out looking nice when using a brush since one needs a very steady hand. An airbrush is better but the results are only as good as your masking. This is also a lot of work.

A quick and very effective way I found uses a Permanent marker. I use a large one that has been well used. The used marker has a softer tip and will slightly conform around a curve.

The permanent marker is drawn around the lip of the window and places a nice even black stripe.

The method to use is to go around the trim once then let it dry. (see diagram) If sections aren't dark enough or need to be made wider go over these sections in one motion. Do not go back and forth over an area or the ink may lift off.

This is usuall one of the last steps in the construction of the model. Excessive handling of the area will wear the black mark off even though it is supposed to be a permanent marker.

Errors
I notice that when I have made a mistake with the marker I can erase the error by polishing that area out. Any of the aftermarket polishing compounds seem to work well (do not use sandpaper only the polishing compound and cloth). It should be noted that the models I used this method on have already been polished out with a polishing kit before applying the marker.

Paint Markers
With the paint markers (ie silver) I guess these can be used also for the window trims.

Glass
Newer cars also have black trim on the glass itself. The same method can be used on the kit windows. For larger areas the black marker generally doesn't work.