The lighting for the top of path blocks is incorrect, they appear much darker while in the ground. When other path blocks are nearby, the central ones will appear much lighter. There is an image attached depicting this.

In addition to this, the path block also gives a light value of 0 while you are standing on top of it in the F3 Debug screen. The same thing happens with soul sand, half slabs, and the lower half of stairs. This likely accounts for various other lighting glitches with these blocks.