Good question. I have also seen first hand the brassy orange and dull bluish gray color of faded old tattoos so I know exactly what you’re talking about. However it think it might be too simplistic to write off the funky faded colors to “cheap pigment.” Cosmetic tattoo pigment is typically formulated with less than a handful of ingredients – the main one being iron oxide and the others being vehicles such as glycerin and alcohol. The variations in the color palette is often what differentiates the pigment lines of all the different manufacturers. As a result, a versatile palette of colors will cover a wide spectrum to suit the many shades of skin color that we all come in and and thus some colors will be cooler in tone while others will be warmer in tone.
Based on my experience I think the orange results from a color that was too warm for the skin it was used on and the bluish gray (or grayish blue) results from a color that was too ashy or cool for the skin it was used on. The main thing to remember is that ALL colors – which includes all types of cosmetic tattoo and regular tattoo ink – are subject to fading and the canvas that it’s implanted into (i.e., living skin) itself is subject to constant change which in turn may also cause changes to the pigment. So like anything else done to alter one’s appearance for the better, a cosmetic tattoo does require ongoing upkeep in the form of touch ups in order to keep the color looking fresh (and not to mention also keeping up with the facial and hair color changes in a person as they get older).