Regarding your illustration, the irony is that because of how computer displays work, that top line is actually very rapidly switching between red and black (the green and blue subpixels next to the red subpixel of each pixel are off), but it is happening with such a high (spatial) frequency, it looks like a solid red line to you.
The difference between those two lines is of degree, not of kind. Both of them are switching on and off. One of them is doing so less frequently. It's a difference to be sure, but there is no objective frequency that, when crossed, changes the nature of it. Any distinction drawn between a line that switches on and off very rapidly, and one that switches on and off less rapidly, is arbitrary (especially when the places where the switches occur can't be controlled). There are no clearly defined two categories here.
The same is true in in time just as it is in space. Movies played on a projector are rapidly switching on and off, but it happens so fast it appears as a steady projection. If I could move fast enough, I could perform two tasks for you "simultaneously" by switching between them so fast you actually see two copies of me in two different places "at once" (though I guess they'd both have 50% opacity).