I've figured out what may have happened!
Firstly thank you Hollie (LOL grumpy bums ahahaha) and Queen Rocks for being understanding unlike the others here who are so quick to jump to assumptions like "I didn't spend time researching the right artist" - my artist has a wonderful reputation or that "I didn't do a quick search" lol as if I would be here if there was a any information out there about tats that darken instead of lighten during healing, which there isn't.
Someone on another forum where I posted the same question (without anyone who jumped straight to "wait and see and stop whining, you irresponsible anxious newbie" routine) mentioned that since I haven't been out in the sun at all but my arm looks browner said perhaps I was having a mild allergic reaction which led to the skin reddening. I've spoken to the artist and switched creams now to something less heavy than the one she initially recommended and that seems to have helped a lot! It's only been a few hours but my skin is less red/dark so will keep using the new light cream.
Thanks again for your help girls!
To the others: keep an open mind, everyone's bodies are different ๐