Reinventing The Tattoo Forum

So I have a client whom I have tattooed many times and I've never had an issue with her skin but recently a piece I did this summer on her forearm and the white healed well in some places but in others it turned this darker almost-her-flesh-tone-but-not colour. I just did another on her other forearm with lots of white (the same white I used on the other one) and it healed perfectly white... I'm confused and I want to fix it but I'm unsure how. Any advice?