I've already mentioned that I'll be using the black permanent market a lot and here is another example for what I've used it. To color in black the power cables that attach to the motherboard as although they are mostly sleeved in black at their end there are still annoying colors like the yellow on the additional 12V power for the motherboard.
These colors can be easily covered, although it still takes some time to do things right, but then you see the end result it looks much better and right as it should be. You can also go for alternative solutions like sleeving with black all these cables, but that is much harder to do and takes much more time, not to mention that you might not have the same good result at the end. And depending on the color composition of your choice you can use different color permanent markers, like green for example that might've also looked good, or maybe red or blue... it is up to you.
The main power cable for the motherboard is much more colorful compared to the additional 12V power, here you have a lot of different colors, but you can as well make them all black and get a great looking result. And because of the much more cables here this connector is harder to paint, not to mention sleeve should you decide to do so.
But how the things look at the end justifies completely the time and effort needed to paint the power cables on the power supply. The only issue here is that you might have trouble should you need to use the warranty of the power supply because of the painted cables. But since the CoolerMaster M1000 power supply also has other issues with the fan not being as silent as it should be I will have to open it anyway and replace the default fan, so the warranty will be gone anyway and the painting was not a problem at all for me.