One approach is to dab on artists acrylics with a brush, let them dry partially, then streak them with a flat brush dampened (not wet) with some alcohol. Be sure to keep the streaks very straight. This takes some practice to develop the right touch, so that you don't take off too much. Work in layers, starting with the more orange shades. After these dry, add smaller amounts of the darker umber colors, let them blend together when making the streak.
Nice thing is, more alcohol can be used to remove the acrylic paint if you want to try over. Usually also a good idea to 'prime' the car with a Dullcote spray, then seal it again with another Dullcote spray when finished.
Caution: too much alcohol can craze the Dullcote. Some modelers actually use that to create a "faded paint" look, but I've heard it can be hard to control. IIRC a webpage by Mike Rose claims that re-applying the Dullcote will 'reverse' the craze effect. You can use another clear flat finish if you don't want to go with Dullcote. Other solvents such as windshield wash or Windex can sometimes work too instead of alcohol.
HTH,
Ed
