Composite video signal

Good day! I am reading some application notes regarding Video Basics:

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I cannot seem to understand Figure 6: Composite Video Waveform. I understand that the IRE levels represent the brightness of the picture. What I cannot comprehend is the representation of the color bars. It shows yellow from 140 to 50 IRE, red from 100 to -20 IRE. The application note also mentions this:

"Color information is added on top of the luma signal and is a sine wave with the colors identified by a specific phase difference between it and the color-burst reference phase."

How does this look exactly on an oscilloscope assuming that the oscilloscope readings are accumulated thru time?

I'm not understanding that if a sine wave "rides" on top of the luma signal, then shouldn't the brightness of the picture also change with the amplitude variation of the sine wave?

Please explain in very basic terms. I find sometimes that explanations are laced with technical terms, and the actual basic explanation is lost. I'd like to get the big picture first before delving into the technical details.


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