Oldschool is one of the oldest Western styles of tattooing. The colors are limited to yellow, red, green, purple and black. Black is used to outline the piece. These thicker lines give way for simple and stylistic subjects.

You might also know this style as American Traditional. A few centuries ago, America was involved in a lot of wars, and sailors and soldiers would sport these tattoos.
Soldiers didn’t only get them as reminders of their loved ones, but also to identify their bodies if they perished.
Because artists wanted to place a lot of these tattoos, there was a large amount of flash tattoos made that every shop would use. It would often be the case that 1 person would do the linework, the other would do the shading and then a third would color the tattoo.

Traditional tattoos don’t use many colors. The illustrative part is mainly based on European designs, but the use of the thick black lines is a technique copied from native tribes. Black ink also proved useful because it hardly fades and kept its form for years. It would also make the subject matter a lot more clear.
Artists were also limited to whichever colors were available at the time.