Although this might seem like a trivial, style based, decision; the truth is that it can have drastic effects on the readers interpretation. If you want more information on why this is so important you can watch this presentation. I will not reiterate the content of their presentation, but I will say that you should consider the information you are presenting when you choose your colormaps. For example, if you have two unique distributions, you will probably want to use a diverging colormaps. You can find all the colormaps and information about when to use them here.