I've seen pictures of DAK soldiers in Tunisia wearing European uniforms. As Tunisia was a temperate zone, did the use of desert uniforms stop then?

I would imagine that the ones who retreated from Libya would still have the tropical kit,the ones arriving in American POW camps captured in Tunisia also seem to have tropical kit.

But,i'm no expert either.

It probably depended on when the troops had arrived and where they had been deployed originally. Those who formed part of the DAK (which had been superseded by the time of 2nd Alamein anyway so the term no longer applies) likely still had at least some tropical kit. Those troops deployed direct to Tunisia would have been equipped according to where they were going. Supplies were always short though as someone kept sinking the supply ships en route so fuel and ammunition tended to be higher priority.

This version of the tropical uniform is almost identical cut to the standard European version: https://s-media-cache-ak0.pinimg.com/736x/d0/94/83/d094830d4de2e34684780c293c09bf02--ww-uniforms-german-uniforms.jpg
Just made from lighter weight material. Even the color, which is described as olive green, would be similar to field-grey in B/W photos.