Decking paint and deck stain solve different problems, and the preview makes the difference visible. Solid deck paint covers completely — it hides gray, patched or mismatched boards and gives you any color a wall could take, but it also hides the grain and shows wear in high-traffic lanes sooner. Semi-transparent stain keeps the grain visible and weathers more gracefully, but it can only darken or warm what is there; it will not turn gray boards white.
The practical rule: if your boards are sound and you like wood looking like wood, preview two or three semi-transparent stains — cedar, walnut, a gray-brown driftwood tone. If the boards are patched, stained or previously painted, preview solid colors instead, and test them against the house body color, not in isolation. A deck reads as part of the elevation: a charcoal deck under warm beige siding sits differently than the same charcoal under white.
Porch floors are their own case. Traditional porch and floor paint in gray, greige or haint-blue-adjacent tones is a classic for a reason — it hides dirt between sweepings and pairs with almost any body color. Run your porch photo through one classic gray and one adventurous color, and the right answer is usually obvious the next morning.