I looked into this a good while back. Only one tartan wearing scots regiment served in the Zulu war and they wore trews - The 91st Foot, Princess Louise's Argyllshire Highlanders.
The other Scottish units wore uniform the same as the rest of the army (i.e. Dark blue) or in one case served as mounted infantry.
There is a plate in the Osprey on the Zulu War and you should be able to google up a pic. The tartan is a dark green with a lighter green square.