What Causes Painless Blue Bump On The Inner Lip?

I am a 27 year old female non smoker who has had a small (about 1-2) cm bump on my inner lip for about a month now. It is not painful and is slightly blue (looks like a black head). I looked at in in the mirror this morning and now it is lighter than the area around it. I thought it was a canker sore, then a cyst, now I am not sure.