The pack is carried in a medium-sized backpack and yes, the backpack is sepia in colour. (I see them to be similar in size as the old style military radio backpacks.)
The equipment is effectively made up of a series of small experiments to determine what aspects of technology actually works on the Shadow being investigated and whether magic functions and if so to what level. The nature of the experiments are set up to be simple and quick to use, so that someone with moderate training could use it in the field.
However due to its size, the amount of testing is therefore limited and is biased towards military applications, such as does gunpowder work, is the use of radio for communication viable, how easy is it for a mage to maintain personal wards for instance.
Even taking this limitation into account, it still give a commander some initial idea of the working parameters of a particular Shadow and react accordingly. If the plan is to spend any significant time on a Shadow, then a more detailed examination of the Shadow can always be carried out to expand upon the initial results of the SEPIA pack.
Due to the usefulness of the SEPIA pack, the other Powers that be are looking into the possibility of developing their own versions.
Additional Note : The Sable Navy has their own version called the SPIT kit, or the Shadow Parameter Index Testing Kit and only differs from the SEPIA pack in a few minor details.