What do I see in the histogram?

[AndreasPhoto]

Hi. I am trying to grasp the consepts of histogram, channels, colors (hue, saturation, brightness, luminance) and so on. Why do the histogram show spikes for both blue and green channel when I have screenshotted a red square with the properties as viewed in the screenshot?

1) I would have guessed that it should only show a spike for red.

2) Am I correct that the histogram show the luminance of colors?

[Rob_Cullen]

I created (a very amateurish) Spark page to explain, in my terms and understanding, "Histograms"

Might be worth a look 🙂

https://spark.adobe.com/page/uJB2ACU1eQzHJ/