The pictures of the largest stars are not realistic, since they show a clear border of a solid object. In reality the out parts are more like a very thin atmosphere. The average density of the whole star is almost vacuum( 1000 times less than earth atmosphere ).
True; an entirely accurate model would be quite time-consuming. For example, a red giant's photosphere is not spherical.
Niel deGrasse Tyson offered the following feedback:
> If the Sun's Wien's law curve peaked just a few Angstroms over from it's current value would you have illustrated it green? But of course there are no green stars even though the curve peaks there for plenty of them.
> The width of the visible part of the spectrum is so narrow compared with the full-breadth energy distribution of the stars that the fractional difference between one color and the next is quite small. The consequence is that we don't actually see all the colors you show.
