The function adds Radial Line Gradation. You can also make a shape by changing the contrast and number.
Prepare an illustration.
Open ①the Layer window and scroll down to ②the bottom. Add ③a new layer.
From ①the Tool Selection window, select ②Filter.
Select ①Radial Line Gradation.
Drag ①the sliders left and right to change the color and number.
To make a shape, set ①the Contrast to 100%. This will create a solid outline for the figure, which can then be used as a background.
Drag ②the thumb to change the position. Tap ③✓ to finish.