I like green for realism, but if your tentacles are blue or even yellow, I'll still flee in terror.
For a complete monsters-and-machines drinking experience, check out the matching Robot Shot Glass.
Sale of this model is on hiatus while Shapeways reboots its ceramic process. As of November 2014 this is predicted to take "a few months". I'm sorry to be vague, it's the best information I have. On the plus side, the upcoming porcelain material is predicted to be generally better and more colorful. Till then!