Really neat idea! I love the rainbow. What is that inside the syringe? At first I thought it was cloth but now I'm thinking paper. Either way, it looks neat!
I think it might be a little better if the focus was on the front colors and the end of the needle, rather than the middle. The shallow depth of field is nice but I would just prefer to see the front part, because I think it would be a better focal point. I also might like to see just a little more of the colors that are coming out, because it seems to be cut off rather abruptly.
I'm trying to think of different ways you could do the rainbow inside. I'm thinking colored sand would look interesting!
Again, awesome idea! Good job!