Elements only give off light when a transition occurs. An electron can be excited by absorbing energy, then when it moves back down an energy level, release the energy as a photon of light. It is mostly metals that give of distinctive colours (such as Sodium) because they have fewer possibly energy states, so more photons released are likely to have the same energy, and therefore the same wavelength. Elements with more possible energy levels give off photons with a range of wavelengths, therefore the colour is less distinctive. As far as I know, all elements have emission spectra.
Humans are made up of thousands of different complex molecules. Elements only give off light when heated (or given energy). Humans would have to be heated (possibly quite a lot), and different elements within the human would take different amounts of energy to excite the electrons, which would then release photons at a range of wavelengths, so you wouldn't really be able to see anything, as the most distinctive coloured emission spectra of metals only occur in trace amounts in the body. Not a great experiment pratically-wise :P