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Vertex Paint
Drag the under line upward.
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Shader Editor
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Add > Input > Color Attribute
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Connect like this.
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Or, like this.
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Select Vertex Paint Mode.
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You can draw,but it's only on the vertex.
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Edit Mode > Edge > Subdivide
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Increase the number of cuts.
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Increase the number of cuts as many as your computer spec allows.
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Now, you can draw on the surface.
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Sculpt Mode is also nice to draw on the surface.
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