In answer to your question the answer is not straightforward.

You can mix pigments that will come reasonably close to skin tone but since the skin changes colour quite a bit with exposure to sunlight, age, temperature etc the match will always be different to that of your own skin.

Also tattoos fade with age so the difference will become much more noticable.

It is not impossible to get a cosmetic tattoo but to be perfectly honest there are many foundation creams that will do a hell of a lot better job.

This is because you can get a much closer match to your own skin tone as there are many more colours that you can use.

Also it is much easier to remove if you do not like the result as you just wipe it off.

Should you still wish to continue I would suggest contacting a dermatologist to put you in contact with a medical tattooist (as apposed to a tattoo artist) they will have much more experience in meeting the demands that is required for this type of ink.

Take Care
Matthew