Hallman goes to great lengths to get the color "right." She uses dry pigments, in powder form, that she applies to paper. When the colors are what she wants she sprays with clear acrylic. She then applies layers of pigment, using tape and applying pressure. She doesn’t use a brush. Then she scrapes away areas to get to color laid down earlier and removes the tape. Sometimes she applies acrylic mediums using the same masking off and tearing up technique. Sometimes she uses color washes and a mix of oil and dry pigment on top of surfaces. I am sure I am muddling how she does this a bit but you get the idea—it is laborious and exacting.
It varies with the piece. You can find out and see more on Hallman at www.terrihallman.com.