Above is a picture of my 318 with the plastic chrome kidneys. At first I really didn't notice it until I started seeing other E30 owners with blacked out grill kidneys. The look started to grow on me and I did it as a little side project while trying to figure out my ellipsoid lights.

The first step is to remove the grill. The left and right sides are held in by two screws and three clips each, the middle grill is held in by two clips at the top. Use a flathead screwdriver to remove the clips on top.

Once you remove the center grill, you can further remove the kidneys with a narrow flathead screwdriver. Be careful not to break any of the plastic clips that hold the kidneys to the grill. Once you remove the kidneys, all you need to do is sand and paint. I actually sort of liked the sanded look since it gave it a brushed aluminum look (unfortunately i can't find the picture that i had that shows the difference).

I picked up some semi-gloss spray paint and gave my kidneys two coats. Be careful when working with spray paint by making sure you are in a well ventilated area.

And the finished product :)