If you are only trying to represent features are shapes and don’t need the color to represent anything, why not choose a color randomly from a palette for nice effect.
I did this in QGIS 3.16, but other versions are likely to be similar.
Start by opening the layer properties:
Select the simple fill, then click on the equation box to the right of the fill color and select edit.
In the expression box enter the following:
array_get( array( '222, 242, 200', '197, 218, 193', '188, 208, 199', '169, 178, 172', '137, 137, 128' ), rand(0,4) )
Each color is represented as an RGB string, you could also use RGBA if you’d like to add transparency. We make an array from the RGB strings, then grab a random item from the array.
To pick colors I suggest checking out coolers.co to generate a palette like the one below.
When you’re done you should have some like what is pictured below.