My first post on this site, and it's about my passion! Tattoos! I have full sleeves and most of my legs covered. Before I was diabetic (T2), I used to heal really well. Diagnosed with diabetes about 5 years ago, and since then, when I've had tattoos, when I get red ink done, it seems to get infected. I've spoken to many people, diabetics and non-diabetics, and this seems to occur quite a lot. I think the fact being diabetic my healing is not as good, and infection is more likely.
I had a Spider-Man tattoo on my thigh and the red didn't get infected in the slightest, but when I got my tattoo of a hawaiin girl on my leg, it got badly infected and my leg swelled up. This was when my diabetes wasn't managed well at all. I had only just found out about my diabetes and acted the normal ignorant way some people do when they don't want to admit they have something as life changing as diabetes.
From my experience of getting tattoos, the better managed your diabetes is, the better the tattoo will heal. Also, with the tattoos being on my legs, as with blood flow, the further away the tattoo is from the heart, the less blood pumps to that area, increasing the infection risk. That's only my experience, i could be wrong.
I must say though, the aftercare is the most important thing, especially for diabetics. It's easy to be a little lapse after a few days of your tattoo healing, but I encourage you to see it through, as it's on you for life. If you;re thinking of getting something small, like writing just in black, then it's just going to heal very easily and quicker. If you plan on a huge tattoo, then that's where you take more care and notice of it.
Edit: Can I also just add that after many hours of painful, and some less painful, tattoos, if my diabetes ever escalated into being insulin dependant, the thought of injecting scares me more than any tattoo! I can take that needle any day!