After basecoating, I applied various darker washes to bring out the shade details.
Loverboy
I used almost entirely Reaper Master Series liner colors for the shading. For Loverboy, it was a thinned-down Purple Liner for the flesh (chosen to give an eerie shade), very, very thin Grey Liner for the white, and Blue Liner (not so thin) for the shirt. I believe the jeans were done with Blue Liner mixed with a bit of black paint.
The Waitress
For the Waitress, I made a thin red wash with red paint and Magic Wash (10% Future in distilled water) and applied that to the dress. I used Reaper Brown Liner for the hair.
The Biker
Not much different here - used a thinned-down black for both the T-shirt and leathers.
The Sheriff
For the Sheriff, I've got the Khaki Triad from Reaper, so I used thinned-down Khaki Shade for the shirt details. For the pants, I used a mixture of Green Liner and Brown Liner. I also went back and applied Brown Liner to some areas of the shirt.