Oil slick color is a style that applies a mix of dark blue, green, and purple tones over darker hair, giving it an iridescent appearance. This is similar to the pastel hair color trend, but its shimmery effect comes from blending darker shades rather than ultra-pale ones. The effect is a darker spectrum of colors all incorporated together with a bit of edge that looks good with really dark roots. (referred to this link; http://www.schwarzkopf.com/en/hair-color/exotic-hair-colors/oilslickcolortherainbowhairtrendforbrunettes.html)
Selfiestar has just released 4 different oil slick colors in 2 styles, SS-176CP and SS-177CP. As you could see at the attached photo, it is hardly for me to find the difference from the salon-technique oil slick color. Save your money for the more important things and try Selfiestar's oil colors.