This aircraft model is so old it doesn't use a material file to control specularity. So it must be hardcoded somewhere that the surface is shiny metal. If you look at the green-painted Ki.61s, you'll see they are very reflective (which is not correct for flat paint). So this baby was just born to fly bare.
The Ki.61 is very underused in AH. It performs better than a P-40, and has a pair of cowl-mounted 20mm that are very effective in snap shots. If you run into a scarily well-flown Ki.61 in the MA, its probably Tongs. And you better have packed your 'chute!