Hey @terrylovejoy, you got it absolutely right!

The last one can be easily produced by just utilizing two different sequences of tonal grading of a specific hue. Those two different sequences would serve as our two different variables. I bet you can imagine there can be multiple different combinations as such sequences can be produced by any given hue.

Thank you so much for dropping by! I just saw you uploaded work so I have to read now ;)

Have a good day!