Blueish colouration after 5th session?

I had my 4th or 5th session a couple months ago and noticed what I thought might be small blisters -- raised bumps that were dark in colour. I assumed they were filled with the dissolving ink. They settled down to be level with the skin but I still notice the blueish colour at the spots where they used to be and am wondering if they're permanent/how to treat them?

Thanks in advance.