My chemistry in school was limited
I remember Chemistry class, when we had to calculate the interaction between two atoms. Atoms, it sounded so cool! I saw atoms everywhere (later turned out I saw eye floaters, which might not be very good). Anyhow, we did just the basic type, 1Hydrogen, and I wanted to move on with 8Oxygen and 94Plutonium 
and stuff. Well, at least 2Helium - the next after Hydrogen. C'mon teacher, I don't need goggles to do theory, it won't explode! But I never got a good answer. Until now. 
Color is the absence of other colors
So what is color? Since sunlight contains all visible frequencies, it turns white. (It's actually off-white #fff5f2, according to this article). And when sunlight hits stuff, some photons get absorbed and some reflected, and the frequency of the reflected light is what we see as color. Nothing special.
Newton is benched
But that's just classical theory. Already with 2 electrons significant corrections have to be made to classical theory. In quantum theory, light isn't reflected by stuff, but a photon is absorbed and re-emitted by an electron. Upon absorption, the electron jumps some distance. How far a jump is determined by the interaction between other electrons and the electric (Coulomb) field of the nucleus. This means that with increasing atomic number the possible interactions get higher and it gets tough already with 2Helium. So far, researchers can model interactions of up to 4-5 electrons. Gold has 79.
The yellow color
Gold has six electron layers and the distance between the last two is hard to determine theoretically. Usually, the gap is calculated to be bigger than experiments show. The transition between these layers lies in the blue spectra, and so blue is absorbed and yellow is left.
Source: Russian magazine Science and Life
Nice article... Although I am not sure it is correct. See my comment below :)
It is actually the opposite to what you mention.
Glad you liked it!
I was just about to comment more on the title that is a bit misleading. This has nothing to do with relativity.
Moreover, after thinking about your article, I am not sure to agree. The atom absorption spectrum equals the atom emission spectrum. Then, a given atom species will absorb light from a particular wavelength and reemit isotropically. This is the color the atoms are. If I am not wrong.
A difference can also occur at the level of molecules, where the emission spectrum could be different from the absorption spectrum.
@justtryme90: do you mind commenting and helping? :)
EDIT: forget what I said (see here). Today I learned something! :D
His paragraph on the bottom is the right idea, it's color is the reflection of non absorbed light, not the emission of energy from energised electrons. The absorption of the light is indeed caused by electrons absorbing light but there are a variety of other non photon emitting radiative and vibrational decay transitions which the electrons can undergo as they go from excited to ground state for release of the energy.
That said I am by no means an expert here. Still AFIK gold is gold because it absorbs blue and leaves behind and reflects the various yellow light, not because it emits yellow photons.
You are right, as shown in the website above. :)
Thanks for commenting.
No problem my friend :)