Something like grass
This brush changes the color of the grass slightly automatically as you draw.
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Activate the watercolor border on your layer for a smooth look.
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You can also use your layer in gray, but it's a bit difficult to use in monochrome mode.
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In this drawing above, I used the grass brush and to give the paper texture I used the following brush: https://assets.clip-studio.com/en-us/detail?id=2134030