Ceiling light fixture has no ground wire, and wires are of same color
It is normal not to have a ground wire if it is a legacy armored cable, which is hard to tell from inside the electrical box. If so is the case, the armoring (metal cladding around the usually cloth insulated wires) acts as grounding.
My house is old and has some of this legacy wiring. I believe one of the wires was originally insulated in black (hot), the other white (neutral), but since it's been 100 years, the dirt has made them both very dark.
To install a fixture on such a box, just put a grounding bolt (or clip) somewhere in the box and pigtail the fixture's ground wire to it and it shouldn't matter which of the hot/neutral wires from the fixture you connect to which of the feeding ones.