Interference Pearls powders are made with mica coated with titanium dioxide. When you look at them straight on they appear more whitish. When viewed at an angles you see glorious irridescent colours. The presence of the difference colours is due to the thickness of the titanium dioxide coating. By varying the coatings you get all the wonderful colours of the rainbow.
Important things to know when working with interference pigment. They are very translucent. The particular colour effect is angle dependent. The strongest colour effect is with a thin application over a dark valued colour, such as black. They can be mixed and blended with other colours, but if blended with a very light valued colour such as white, they will all but disappear and the interference effect will be blocked. However, this is a ratio dependent effect, and one can create subtle interference and iridescent effects by adding very small additions of white or other opaque and light valued colours. If mixed with darker valued colours, they will make an infinite variety of iridescent colours. You can blend them with any translucent acrylic medium to create iridescent/interference or nail polish