Magic Tattoos

Magic Tattoos exist in both permanent and temporary forms. 
Temporary magic tattoos are made of henna infused with gemstone dust and permanent tattoos are made of a special resin infused with gem dust. The tattoos are applied in conjunction with a special song and the song is truly what makes the tattoos magical, as it works by magically activating the imagery created. The song must be sung or hummed throughout the procedure, which is usually why it takes 2 or more people to complete a magical tattoo. 
In the case of the temporary tattoos, the magic lasts about 2 weeks, after which the images fade and they have to be reapplied. It is applied much faster than in the case of a permanent one, and typically only one person is required to apply the tattoo. 
In the case of permanent tattoos, it is common for two or more people to be present to complete the application. After which the tattoo becomes activated, turning the colour of the gem dust that was infused. 
Both tattoo types must be applied by an expert, and only one magical effect can work on an individual at any one time. It is possible to dispel the magic of the tattoo as well, but it requires at least a 5th level spell or a DC18 WIS roll to permanently disable the tattoo. If the magic tattoo is disabled, the tattoo itself vanishes. 
The table below shows the gem colours and effects, as well as the gold cost. 

Gem Type (gold cost - temporary)	Gem Type (gold cost - permanent)	Application Time (Temporary)	Application Time (Permanent)	Effect
Sapphire (1000gp)	Sapphire (5000gp)	1 hour	8 hours	Resistance to cold damage
Ruby (1000gp)	Ruby (5000gp)	1 hour	8 hours	Resistance to fire damage
Topaz (1000gp)	Topaz (5000gp)	1 hour	8 hours	Resistance to lightning damage
Opal (1000gp)	Opal (5000gp)	1 hour	8 hours	Resistance to thunder damage
Amethyst (1000gp)	Amethyst (5000gp)	1 hour	8 hours	Resistance to poison damage
Rose Quartz (1000gp)	Rose Quartz (5000gp)	1 hour	8 hours	Resistance to psychic damage
Obsidian (1000gp)	Obsidian (5000gp)	1 hour	8 hours	Resistance to necrotic damage
Emerald (1000gp)	Emerald (5000gp)	1 hour	8 hours	Resistance to acid damage

The gem dust can be replaced in part or in full with the equivalent amount of Eidonite.

Access & Availability

It is more common to see temporary magic tattoos, but permanent tattoos can be spotted on quite a number of people as well.
It is likely, especially in Ile Ile, for a magic tattoo to be gifted to a champion or a particularly favoured individual of a leader. Though to find someone who is skilled in applying these tattoos... that is much harder.

Discovery

The origin of tattoos cannot be traced to just one culture, as people from Yana Inti, The Johin and Ile-Ile all seem to have been doing tattoos independently for millennia.
The infusion of gem dust and magic into tattoos, however, came from the Kha elves who merged their practices into Ile culture.