Image: Alan Friedman of Averted Imagination
Alan Friedman, a greeting cards-maker by day and astronomer by night, took this amazing photo of the Sun. APOD explains why it's blue:
Our Sun may look like all soft and fluffy, but it's not. Our Sun is an extremely large ball of bubbling hot gas, mostly hydrogen gas. The above picture of our Sun was taken last month in a specific red color of light emitted by hydrogen gas called Hydrogen-alpha and then color inverted to appear blue. In this light, details of the Sun's chromosphere are particularly visible, highlighting numerous thin tubes of magnetically-confined hot gas known as spicules rising from the Sun like bristles from a shag carpet. Our Sun glows because it is hot, but it is not on fire. Fire is the rapid acquisition of oxygen, and there is very little oxygen on the Sun. The energy source of our Sun is the nuclear fusion of hydrogen into helium deep within its core. No sunspots or large active regions were visible on the Sun this day, although some solar prominences are visible around the edges.
For a larger pic, be sure to check out APOD: Link
I have seen these types of pictures in the original hydrogen alpha red. I suppose making it blue makes it easier to pick out details, though I suspect it is less about science and more about the photographer liking the color blue.