Here's the node layout for the first shader. This one is the floor of the first image. The shader starts with the ambient occlusion node, which we then filter through a math power function. This takes the square root of the AO output, which just softens the transition between light and dark areas of the AO node. After that, we subtract the output from 1 with another math node. This just inverts the colour, so now we have white in the places where we want dirt and black in the places where we don't. From there, we take the output to the bias parameter of a clouds node. By doing this, we tell the clouds node to make white cloudy bits where we want dirt and blackness everywhere else. Finally, we use the output of the clouds node to drive a blender, with dark green for dirt and white for clean areas.

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