I recently acquired a Tuffli class freighter. On the back of the freighter are 2 warp engines, 1 on either side. I've equipped this freighter with both the mark XI engine from the Jem Hadar space set and the Borg assimilated engine from the stf merchant. When the Jem Hadar engine was equipped both engines had purple light coming out of them. This is typical of all the ships I've equipped the engine on. When I equipped the assimilated engine only the left engine turned green. The right one was the default color blue. I found it to be distracting.