Colorz AKA colors have special meaning to the Greenskins (Orcs & Goblins and Orks) of Warhammer Fantasy and Warhammer 40000. It has origins in the original comedic elements of Warhammer, with the greenskins heavily influenced by
soccer football hooligans during the 70's-90's when rowdiness and fanatical obsession lead to frequent riots and embarrassing mania; sports teams and fans are generally superstitious.
In Fantasy this works through magic and actually functions in a way that other races (or at least Wizards) can observe and understand. In 40k this occurs because all Orks share a psychic link allowing them to impose belief on reality (making an engine and cockpit made of random metal welded together and partially held together with sinew and feces into a functional aircraft for example). Thus for them, simply painting something is the same as engineered or enchanted upgrades for other races. Body paint or a skin mutation is likewise an amazing thing. Sky color, water color, any color has meaning.
Belief in Colorz is instinctive as greenskins are simply an apelike race that reproduce by dying and releasing zygote spores like a fungus, who are "born" with all the knowledge they mostly need including speech and belief in their various gods. The old Fantasy continuity when Orcs had females and young as well as could breed with humans predates Colorz.
Objects or beings that are red go faster. Red can also be described as brutal since since going faster helps get into melee. The most well-known and mematic color, because "Red goes fasta." Believed to have started as a reference to the first "Gundam" anime of all things.
Blue things are lucky. This goes both for safety and gain. Blue is also cunning, and in Fantasy represents magic itself as well as the physical protection that magic warpaint brings to Savage Orcs.
The best, because it is their own natural skin color. Anything can be improved with green, even if other colors actually add powers. Fantasy greenskins may paint their non-greenskin allies like Giants and Ogres green to help them be Orcy while Orks paint their human allies, the Diggaz, green as well. Any attempt at diplomacy should involve the color green.
Wealth, although not because of gold; Orc/ks use Teef (teeth) as currency, and their teeth yellow fast. Orks also believe yellow produces better explosions, while Orcs do have a slight value for precious metals although they mostly just pile it up as a luck totem to bring better loot and Teef (it works).
Death, like bones. White is dangerous, and can have multiple meanings although generally it means fearlessness and intent to kill.
Toughness. Black Orcs get their name as a description (that and the fact their metal armor tends to be tarnished and blackened) rather than the color their bodies are due to this. Black things are hard and durable. (Bow chica bow wow.)
Regardless if it actually matches the environment, greenskins who think they have camo on will actually seem near invisible. Likewise they may not register camo that they see.
Checkerboard patterns, usually white and black, can mean a connection to Gork and Mork (or was it Mork and Gork?), increased physical prowess, or is a means of showing allegiance; in 40k checker patterns mark an Ork as belonging to the Goff Klan (clan) but in Fantasy the meaning is less clear. A popular meme is that it is Orc/K camo attempts with white being daytime camo and black as nighttime camo.
A purely meme color. At one point the community noticed no Games Workshop paintjob had yet featured purple, and fans began to joke that its because purple is for the greenskins stealthier than using camo, and more cunning than those using blue since nobody had ever seen a purple Orc/k. It has been repeated as if fully canon for long enough GW itself has taken notice; in interviews writers have mentioned it, and several mentions have been made as jokes in Black Library works. *UPDATE* Duncan Rhodes brought it up as a camouflage color for Orks in a recent video so... yeah, it's canon now.