Well you’re right that there is colour in the “sky” spectrogram, but if you loop the dark segment (easy in audacity) you will hear that it’s just background noise. The “Kindern” sample has had noise removed or been recorded in a studio setting. It’s also worth bearing in mind the colours are on a log scale; if you switch over to looking at the waveform you can see just how little is going on in both of those little gaps.

If this interests you there’s a whole world of phonology and linguistics out there waiting for you… my mind was blown as a teenager when I learned about ich-Laut and ach-Laut.