I started by using some fine sandpaper to rough the top surface of the heat sync so the spray paint would adhere a bit better to as I didn't have any primer. I then washed it off to remove any grit and dust that had come from roughing it.
The next stage was to stick like a newspaper skirt around the heat spreader second from the top using tape (I was going to use masking tape but forgot to but some so just used electrical tape instead as I knew it would come off easily again and not leave residue). Once covered, I sprayed it with two quick coats of satin black paint and left it to dry for about 1 hour. Then proceeded to fit it to my rig. Here's some pictures below what do you guys think of it?
(sorry about the awful quality of some of my photos, my phone struggles in some of the lighting so you can't properly see the full effect once the cooler is fitted.)
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