Why can't stars be multicolored like gas giants?
Gas giants like Jupiter and Saturn have bands of different colors in their atmosphere. These are due to the rotation of the planets. Stars rotate too, so why do most stars have patches/blotches of color rather than having latitudinal stripes?
The bands on Jupiter and Saturn are caused by the rotation but the colors are caused by the atmospheric composition. Stars *do* have different colors, but this is caused by the different temperature for 2-3000 K for red dwarfs to 30,000+K for blue supergiants
Also, gas giants' appearance is due to reflected light, whereas the light of stars is due to their own radiation. Reflected light tends to vary more with material composition than does the blackbody radiation that comes off a hot object like a star.
I think it's premature to ask this on account of our limited ability to get high-resolution full-spectrum images of any star other than our own.
Just rotation is the wrong tree to bark up on.
You see color variations on gas giants due to differences in composition, i.e. ammonia vs. sulfuric acid clouds on Jupiter, which are transported differently on the rotating planet in the up/downwelling bands.
Spots on stars originate due to very different physics. At the temperatures which are prevalent on stellar surfaces, molecules are mostly dissociated and ionized, we call this state a plasma, so no more colour effects due to ammonia or others. Star spots are concentrations of the local magnetic field, which is coupled to the plasma dynamics. The magnetic field pushes the gas aside and lets the surface cool locally. This makes dark spots that you see on stars like our sun.
There is a transition region in terms of surface temperature of 2000-3000K, at the masses of brown dwarves. Those failed stars seem to exhibit dark bands on their surfaces, which are thought to be due to absorption from exotic, high-temperature molecules like TiO and VO (Titanium and Vanadium oxide).
Great answer +1 In short, the laws of coloring for stars are governed by temperature, not composition.
Can you clarify this sentence "*Star spots are concentrations of the local magnetic field, which is coupled to the plasma dynamics, pushes it aside and lets the surface cool locally.*"? It's not grammatically correct at the moment so I can't parse exactly what it is trying to say.
@TylerH: Star spots are concentrations of the local magnetic field, which is coupled to the plasma dynamics. The magnetic field pushes the gas aside and lets the surface cool locally.
Can you clarify what you mean by "pushes the gas aside"? That doesn't match my understanding of how sunspots work. (But then, my understanding is that it's still not a well understood phenomenon.) Apart from that sentence, I think this is an excellent answer.
@craq: That depends on which level of detail you're asking about. The basic physics of sunspots is very well understood. Their coupling to the global magnetic field, particularly for stars other than the sun is still in active research. The magnetic field usually follows the plasma flow (frozen-in property of MHD plasmas), but nonetheless slowly diffuses and 'bubbles up' relative to the gas. Once the magnetic energy is sufficiently concentrated in a region, it acts as additional pressure in the Navier-Stokes equation, i.e. the total pressure gradient becomes $\nabla(P+B^2/2\mu_0)$.