It didn't explain the picture.
In this experiment, the electrons interact with the photons to produce quantum energy packets, which the microscope detects. What is the colour of the quantum energy packets? The question has no meaning, because they aren't light. Since the colour is arbitrary, they can choose to colour it in any way they find useful.
Having said that, I also don't understand the "photograph".
Actually, we do, so long as that energy is in the form of photons [1].
[1] http://www.nature.com/news/people-can-sense-single-photons-1...
Of a particular range of frequencies
For each electron fired at the wire, it can either pass through unscathed, or it can interact with an electron and scatter off with a different energy, like two billiard balls hitting each other. The collision is fundamentally a collision between two particles. However, the fact that the properties of the collisions vary sinusoidally along the length of the wire imply that the photon is also acting like a wave oscillating up and down the wire.
I disagree that this is the "first time" that we've observed simultaneous wave-particle behavior, you can see the same thing by firing photons at two narrowly-placed slits. This results in a diffraction pattern as if the photons were interfering like waves, but we can confirm that we're detecting single photons at the detector, and you can even confirm that each photon travels through one slit or the other ... See https://en.wikipedia.org/wiki/Double-slit_experiment