This subject is open to a lot of debate. That being said, as of February 18, 1943 "dark yellow" was the base colour for all vehicles leaving the production lines. I'm not sure what, if any, reinforcements were sent to Tunisia after this date so can't say if this colour appeared in the desert.
Vehicles before said date were sent to north africa in the standard panzer grey and were later in the field modified with desert paint colours. In 1943 these would be Braun RAL 8020 with Grau RAL 7027 used as an optional camou pattern.
There was also mention of tigers being a dark green or even olive colour. These were most likely panzer grey with an overspray of olive-green which gave it's dark green appearance.
As for paint manufactures, there is a few to choose from: Testors, White Ensign Models, Life Color Paints, Xtracolor, Xtracrylix, Agama. If anyone knows of others, please do chip in.
Some articles to read:
http://www.panzerworld.net/colours
http://www.achtungpanzer.com/articles/camo.htm
Jack