Erlkönig Camo

WORK IN PROGRESS
This article is a draft and will see updates in the future, including illustrations and some editing passes for the text to make it more concise (hopefully).

When attempting to avoid detection by a hostile AI, machines have for the most part continued the "traditions" which were designed by humans and their researchers. These methods cover the different ways of detection - in the most basic sense, camouflage aims to prevent being seen. Other forms of detection, like being heard, can be mitigated with certain behaviors as well. All of these methods however assume the sensory perception of a human, or at least common mammal. Machines, while following that "template" for the most part due to their original creators being humans, however can have an expanded range of senses that are hard to counter with commonplace strategies...

Tried And Tested

Tanks in particular consider covering their frames in camo paint something mundane. It's seen as an ordinary part of regular maintenance routines that is, nevertheless, a vital part that not only warrants but outright requires special care. The philosophies of what makes the most effective pattern of paint vary greatly and feasibility of the preferred patterns depends a lot on what material is available to the individual applying it. The region that the tank inhabits and its particular environmental conditions play an important role as well - tanks living in areas that have winters rich in snow will need to take into consideration that they'll need to adjust their camo paint to at least two different seasons. Sometimes, a tank that is not in immediate danger of being ambushed or in need of ambushing others may favor a pattern that isn't entirely practical but fulfills another (usually social) function.
In general, most tanks agree, though: Even if it's not always easy, conscientious efforts should be made to achieve this most basic of protection levels. Rolling around in one's factory coat and expecting other machines to ignore you is an act of willfully lowering the average life expectancy.

...Except When It Isn't

As widespread and effective these camouflage paint patterns may be for the average tank, their concept is firmly rooted in the assumption of whoever is trying to detect them having to rely on mammal-like vision. Since the general, average ability to visually detect another being when using their optical sensors is based on similar principles in tanks as it was in humans, the same essential principles also apply when a tank is trying to hide from another tank's optics.
In conditions that wouldn't lead to detection through other senses anyway, blending in with the surroundings by matching their colors closely and holding still or moving sneakily can be assumed to be completely sufficient. However, this concept crashes and burns entirely when an AI is encountered that doesn't need to rely on the principles of human-like vision to "see".
The most common example of such alternative vision systems are the ultrasound-based sights used prominently by SPGs. They use an echolocation-like method to construct virtual images of their surroundings, with the waves even able to penetrate certain otherwise opaque obstacles in their line-of-sight. Complex calculations to interpret the feedback received that way are then done to figure out if there's potential targets present. In the absence of a forward observer supplying them with first-hand target information, a skillfull user of these special sights can find otherwise obscured target amost effortlessly. But while this technique makes traditional camouflage paint void, it can still be countered with pretty simple measures. Makeshift camo, particularly adding large amounts of foliage to one's frame, is considered efficient since it helps make a tank look a lot less tank-shaped from a distance this way.

Erl-King's Revival

Unfortunately for any tank that learned to sit still and expect to evade being seen like this, other vision systems aren't fooled at all by such - to them - trivial ploys. For a machine that is using thermal sights, for example, the task of spotting and killing enemies trying to use traditional camouflage methods becomes one of shooting fish in a barrel.
With the drastic decline of available equipment and its technological standards, and maintenance being a constant challenge, it's become a seldom enough occurence to meet such an AI, however, that the majority of the known world's inhabitants can reasonably gamble on never meeting one during their lifetime. Or, if they might, the odds of it happening are small enough that not worrying about them in their daily life is justifyable. They have many, many other things to worry about.
To tanks who have had this sort of encounter (perhaps even more than once), or those who even possess that kind of technology themselves, the issue - understandably - is weighing a lot heavier on their mind. An at times obsessive preoccupation with the futility of trying to hide from advanced senses would eventually lead to an entire different style of camouflage emerging. Being seen may be inevitable, but being perceived isn't. The awareness that visual trickery might fool regular optics and perhaps even artillery sights, but not thermal ones.
In a similar vein of how battleships use dazzle camouflage to disguise their dimensions and course, and in a similar vein of how changing one's silhouette can conceal one's tank-shaped form, some tanks started to rethink their approach to camouflaging themselves....entirely.

Hiding - in Plain Sight.

Instead of trying to conceal their presence, these machines decided that if they cannot avoid detection at all, they're going to do everything in their power to appear as anything else but themself. Tanks with small frames will try to add bulky add-on armor to scare off others. A tough frame with thick armor plates will have its paint expose a layer of rust on purpose, or random worn-out parts affixed to it in order to appear brittle and bait weaker attackers. Valuable components will be covered up in rags or flimsy-looking sheets of thin metal. Entire hulls and especially cannons will be painted in erratic-seeming patterns and colors that clash with the environment or the rest of the tank, in order to confuse potential attackers or at least make it more difficult to properly assess the true threat level of their target. The heat signature of an engine or exhausts will be masked by carrying around warm or cold objects (like fresh roadkill, ceramic heaters, or containers with boiling/frozen water, for example) - though the effectiveness of that method is disputed. Some more creative individuals have come up with more "outlandish" ideas like taping/glueing aluminium foil, or ceramic/glass shards onto their frames in an attempt to hide the heat radiating from their internal components.
In general, the goal of this special type of camouflage is not to create an illusion that is convincing on closer scrutiny - it only needs to make the wearer easier to miss on first glance. From up close, when viewed through regular optical sensors, these measures will make the wearer of the camouflage look messy, worn-down, weird, or even ridiculous in the opinion of other tanks not prescribing to their ideas of effective disguises. Some of them may look entirely unrecognizable as a tank - but in a way, that's exactly what they're trying to achieve, after all.

Origin of the name

The term "Erlkönig camo" is widely used by the machines, though no one really knows who first started using it or if there's any particular history to the term.
Sometimes, if a tank has a particularly ragged appearance or a taste in camo patterns/colors that their peers consider outlandish, they will teasingly call it Erlkönig camo, as well.