The Fortbyte number 28 is quite special. First, head to the desert junkyard south of Paradise Palm (see map below).
At the east end of the junkyard, you will find a lever and several colored panels leaning against a wall. Once the lever is activated a sequence of colors/notes will be played on the panels. You will have to reproduce the exact same sequence.
In total you have to play 3 sequences, each time a little longer than the previous one but always with the same first notes. You must not make any mistakes if you want to unlock the Fortbyte.