Needle depth can have a profound effect on the appearance of your healed tattoo; this is due to the unique characteristics of human skin. If the pigment is not implanted at the correct depth within the dermis, then a blue/grey/green colour can appear, this is due to depth-related injuries that occur in the skin.
Additionally, the type of tattoo equipment the artist used throughout the treatment is also very important when it comes to your healed results. A depth-related colour change may be due to a lower precision digital tattoo machine being used instead of a high precision one.
Low-quality machines tend to implant pigment in various depths instead of a consistent flow.
Lastly, cosmetic tattooing has been around for decades, and many things have changed over time, the development of technology has been profound in the cosmetic tattooing industry. Although artists once use pigments that would overly oxidise, creating a grey/ blue tone.
With new standards and regulations in place pigments that overly oxidise should not be used nor allowed; instead, the cosmetic tattoo artist should ensure they match the pigment to your skin tone.