Repetition and patterns are created by the alternating shapes. The colours alternate as well, with dark and light shades and hues. The activity encourages children to observe the order of shapes and colours.
I remember pinning one such idea here https://in.pinterest.com/pin/74872412526283660/
We will need two toilet paper rolls to create the shapes and two shades of poster /gouache paints.
Drawing a grid makes it easy to print.
The shapes can be filled by smudging in the wet paint without distorting.