[thisrod]

People do take photographs of single atoms. It requires a very colorful atom and a very bright flash, but both those things exist. They're not particularly interesting photographs: atoms are smaller than a light wavelength and they look like dots. I've seen them before, although I couldn't find one in a minute of Googling. There are even movies, as described in this paper:

http://dx.doi.org/10.1063/1.36788

[weinzierl]

Abstract:

   We demonstrated interruptions of macroscopic duration in 
   a single trapped and cooled Ba+ ions’s 493‐nm 
   fluorescence. They are caused by transitions of the ion 
   into the ‘‘dark’’ 2D5/2 state.—Multiple simultaneous 
   jumps of three ions indicate cooperative interaction 
   with the light.

I haven't read the paper but I'd be interested in a quote from the part that supports the statement: "People do take photographs of single atoms. It requires a very colorful atom and a very bright flash,..."

I'm not aware of a definition of atomic color but maybe that's a real thing in analytical chemistry, spectroscopy or some other field. I wouldn't be surprised.

Probably it's just the wavelength of the emitted light.