The colored contact lenses slipping in your eyes is the same problems as eyeglasses slipping from your nose. This is usually caused by a size problems of the lens. You may wearing the improper sized colored lenses. Or, you it is because of your improperly inserting contact lenses. Besides, if you often rub your eyes, it is also likely cause the slipping of the contact lenses in your eyes.
If your contact lenses have been prescribed and fitted by a lens specialist, then they should not be slipping down your eye. Many cosmetic contact lenses like colored contact leses may be sold in just one size that may slip constantly. i guess you don't have a lens fitting before buying contacts.