The xxx.OB files are open bus files.  00 through ff were loaded into the PPU, then the register was read.  This is the result.
The xxx.PAL files contain the 8 bit and original 3 bit data for each palette entry, 0-3F.  The data is repeated 8x with various emphasis bits
turned on.
The xxxM.PAL files are the same, but with the mono bit turned on too.

note: the P2C04_4 chip appears to have problems with emphasis bits.  this is true across 3 samples of the chip.  the others work as expected.