Sorry for my short note: I love your question, because I had not thought about it. Your invitation is very much attractive. I shall think about it and then try to provide a reasonable answer. Thank you for your question, dear Sandeep!

Well, first of all, absolute zero is just a model, not a real physical state of a body. You would need an infinite ammount of energy to cool a body down to 0, and even in this case you would have a zero state quantum fluctuations because the product of impulse and position must be above 0. 

To the colour - if the electromagnetical spectrum of a observed object does not include the short range of wavelengths that is visible for human eyes, it appears black. 

i think it should be hidden ... at absolute zero 

the body does not interact with any other objects ....

i appriaciate comments of Carlos Eduardo Maldonado. thank you sir.  Dear Sachar Ichilmann, sir I am very confused for absolute zero. 

All matter emits electromagnetic radiation when it has a temperature above absolute zero. do they emit radiations below this? (say -500K) if yes, how to calculate their emission if emissivity known.

In addition, (University Munich and the Max Planck Institute of Quantum Optics in Garching have now created an atomic gas in the lab that has nonetheless negative Kelvin values (Science, Jan 4, 2013).

Read more at: http://phys.org/news/2013-01-atoms-negative-absolute-temperature-hottest.html#jCp

2.using Weins law we can calculate peak wavelength. example: Radiation from mammals and the living human body: Mammals at roughly 300 K emit in the far infrared.

considering this example, if go on either heating or cooling any object (in suitable controlled atmosphere) will it emit radiations other than thermal? Like, will it emit microwaves,radio waves or other side UV and x,gamma etc.

Please let me know your opinion about this 

1.Actually, I am interested to know the fact that at 0K molecular momentum is zero. so body may not emit anything I agree. yes! below 0K temp is possible now so definitely molecular momentum wont be zero , i suppose there should be some emissions,it will depends on number of other parameters. I am taking comments from experts. please give ur comment too.

2. with reference to following fig. I think, emissions from bodies at any finite temperature can be in a complete spectrum from cosmic to radio .. if we heat or cool it (say at 30000K much more than Sun's temp) it may emit X to Radio... is it really possible ?

Please reply

According to Wein's displacement law of radition, for lower values of T (approaching to zero) wave lenth becomes infinity or very large. At those values of wave length radiation intensity or emissive power becomes minimum and hence the body apprears to black with nacked eye. 

Dear All,

The question itself is interesting on the face of it, but problematic for a number of reasons.

First, the concept of zero temperature is only intuitive for particles (massive or massless, like photons). Temperature is an abstract concept and its more fundamental definition (in equilibrium or close to it) is as the change in energy as the entropy changes. This is, by the way, why one can have negative temperatures in some systems. With this in mind, you see that by emitting radiation the body's energy would change and hence its entropy, which means that the temperature is not zero really. Conversely, the only way to emit radiation and still be at zero temperature is if the number of microstates of the body is truly infinite and hence cannot change. Sorry, if this sounds too abstract, but this is because the concept of temperature is abstract.

Second, one could argue that colour can also come from reflection of radiation from a source external to the body at zero temperature. This means that at least one photon would hit the body and then be reflected into the observer's eye. However, if this happens, the body would recoil, if ever so slightly. This means that its kinetic energy have changed and we are back at the previous case, namely, this would lead to a change in temperature unless the number of equilibrium states it is in are truly infinite to begin with.

So, the question is not well posed because seeing the colour of the body already means it is not at zero temperature!

This is a little like asking, what is the color of a red balloon inside a totally dark room. 

0 K is different from absolute zero so at absolute zero it will behave like a black body. However at 0 K it will have some color depending on the material properties.

Don't forget that photons have momentum, which would give finite temperature to a body at absolute zero. One question might be, what is the absorption coefficient at the frequency of interest, and what is the rate of change of the absorption coefficient as a function of temperature?

When approaching absolute zero a body reduces its thermal radiation becoming less and less visible.

The body still has electrons spinning at their levels of energy, so the emitted photons would be pure perturbed states of the outer electrons of the body, carbon would be black, etc..