Tribal tattoos are a common form of sleeve tattoo. They are almost always done in solid black, as this is the color of ink that original tribal tattoos -- ones that were actually worn in tribes -- would have been. Tribal and neo-tribal tattoos tend to refer to a certain kind of tribal tattoo, featuring thick lines, which often curve and curl and always taper to end in a point. However, tattoos from specific tribal areas have also become popular, such as Maori and Polynesian tattoos.
Bio-mechanical tattoos are inspired by the artwork of H.R. Giger. They are concerned with the fusion of man and machine. A popular concept for bio-mechanical tattoo art is to make it look as though there is a tear in your skin, and below the skin lie wires, circuitry, a metallic skeleton or similar. Another common bio-mechanical sleeve theme is the fusion of flesh and machine. This style of tattooing is normally done in black and gray, but some add color.
Japanese designs are hugely popular for tattoo sleeves, and can be made to look masculine or feminine. Although they are often done in color, they work just as well in black and gray. Japanese tattoos either have waves or wind bars. Those with waves commonly feature koi fish, and those with wind bars often have foo dogs or dragons on them. Cherry blossom and maple leaves are a regular find on either variety.
Religious sleeves can be found in color or black. Common Christian themes include the ascension, angels and demons, the virgin Mary and rosary beads. Buddhist tattoos are also quite common. However, tattoos aren't allowed in Islam or Judaism. It's debated whether it's OK for Christians to be tattooed, as there some ambiguous passages about it in the Bible. Some people, though, just get religious tattoos because they enjoy the imagery, rather than because they are religious.