I used paint from Home depot.
2 thin coats of primer and 2 thin coats of Ralph Lauren River Rock paint.
The track was first flamed with a torch and high oxygen content flame.Barely kiss the track with the end of the flame and keep the flame moving at all times. you will notice a shadowing effect on the plastic which is all you are trying to accomplish. Let cool a minute or 2 and then Prime.
Primer was painted so thin as to be translucent. Allow 2 hours to dry and paint second coat very thin. Let dry overnight.
Paint very thin coat of finish paint, let dry 2 hours. Paint 2nd coat of finish paint wait 2 hours and remove any masking tape. Let paint cure 3-4 days minimum before use.
I used a foam brush and thinned my paint and primer abprox 50/50 with water.
After curing I weather with a mix of 1 cup of 91% Rubbing Alcohol (available at better pharmacies) with a few drop of Higgins India Ink. (use a test piece of track and start with 2-3 drops...add more as you desire for darker or just recoat track to darken.
Here is a comparison