I have been painting Night Lords since the second edition, and in my opinion, they might be the most challenging Legion in the Horus Heresy when it comes to painting. I have reworked my models many times because I simply haven't found a colour scheme that I am truly happy with. Of course, the choice of bits plays a major role from the very beginning. The gap between a wide selection of more neutral 30k bits and overly elaborate, bloody skin flaps and wings is so narrow that, over the last few years, I have either seen a lot of evil Ultramarines or bloody Cringelords. There are several aspects of painting them that I find particularly challenging.
1. Midnight blue. Hardly any Legion has such challenging colour transitions in its primary colour as the Night Lords. Midnight blue ranges from almost black in the deepest recesses to a vivid blue-green in the highlights. Without proper airbrush application, this is difficult to achieve, which is probably why I have seen so many evil Ultramarines in Dark blue.
2. Lightning. Light effects on miniatures are extremely challenging—at least for me. Lightning is an essential part of the Night Lords aesthetic and is practically indispensable. Most of the time, however, I don't see Night Lords with lightning; I see models with white brush strokes. My own models have very little lightning because I am simply terrible at painting it.
3. Skin. Skin and body parts are especially common among the elite units. They create an absolute contrast to the armour and are challenging because the bright skin immediately draws the viewer's attention. What does dried skin actually look like? Is it preserved, and if so, with what? Does such a preservative exist in our world? Is the skin fresh? Is it older? If I can't paint flayed skin properly, I end up ruining the whole model because of the strong contrast.
4. Decals. The Night Lords have some fantastic decals, but the decal sheet—with its red and black designs—doesn't really complement the large areas of the primary colour. Then there is the contrast created by the red. Those vicious, dark murderers can very quickly end up looking like people dressed for Halloween.
5. Blood. While some people seem to dunk their entire model in blood and gore, it already seems difficult enough to add blood effects to preserved skin convincingly. Many paint and hobby manufacturers promote dedicated products for creating blood effects. But as soon as you overdo it, you inevitably start drifting towards the absolute Cringelords.
I still take a lot of time when painting my Night Lords, but naturally that means I don't make progress very quickly, and I'm not always happy with my results. Nevertheless, I'm happy for everyone who has fun with the Night Lords and enjoys the hobby. Feel free to share whether you've experienced similar difficulties and whether you have any tips.