Today it was raining so I went out to catch some fog. Unfortunately I . . .

My first is a color, or the absence of light. My last follows 'snail', as it moves slower than a modern track. Together, I use knowledge to extort you, to my delight.

I am a clock that hates the dark, dependent on the sunlight’s mark.

I am a boundary with no wall, A door with no hinges, A keeper of light and secrets. When I part, another world appears.

I am a dark shape against the light, with no fine features shown in sight. Not the shadow cast at your feet, just your outline, dark and neat.