Since Cal is a Jedi in hiding, he could not wear a Jedi robe. We could however hint at his Jedi roots in the silhouette by introducing him wearing a poncho. The poncho made sense for the rainy environment in Bracca but it posed a long set of challenges on the technical and character rigging sides. The poncho was an additional challenge for a character who was already performing agile exploration, combat and would eventually carry a droid on his back. In addition, the cloth had to work withing memory budget without causing performance drops and it had to work with the character rig.
The solution resulted in a compromise in length. It respected the anchor points for BD-1 to hold onto and it also included side openings to provide access to the lightsaber.
The material is rain resistant. The color palette, with it's large orange color blocking, references some of Ralph Mcquarrie's designs. The graphics and insignia reflect his ship rigging crew and his employee number.