How to mimic the distressed or marbled look of leather or vinyl?

A marbled or distressed appearance is easily mimicked with a damp sponge and a spray bottle of water. You can work with one color or two. Most folks simply play up the difference between the original stained or faded color and the new color by applying one thin coat to the entire piece and then printing or stippling additional coats on 80-90% of the surface.

The trick is not so much how you apply a new finish, but how you disperse it. You can also thin or strip some of your work, if needed. This video demonstrates.

Some tips:

• Dilute Color with Clear Prep+Finish™ to make a glaze. This makes the color more transparent and easier to blend, especially with noticeably different colors (i.e. printing a dark brown over a light tan).
• Spritz the surface with a little water to allow the color or glaze to follow a natural chaos. It also increases your working time before the color begins to dry.
• Use one sponge to apply; use a second to disperse and blend. Leave some areas thin or even untouched.
• Disperse and blend the color before it dries to avoid any harsh lines or marks.
• Periodically step back and assess the appearance from afar to ensure you’re not overworking any area and getting too monochromatic (solid appearance).
• Come back with a dirty sponge (but not much glaze) for missed nooks and crannies.
• For a very defined print over the base color, use a paintbrush to apply the color or glaze to your sponge. This results in a cleaner, finer print. Saturating the sponge will lay the color on too heavily and therefore obscure more of the base color.
• For a burnished appearance, concentrate the color along seams, piping / welting, or tufted buttons, and blend outward. 
• The color will erase more easily from non-absorbent, finished leathers. Try a rag with water or rubbing alcohol. You can also dry or wet sand with 500 grit sandpaper or a ScotchBrite® pad.

Heidi beautifully demonstrates a sponge and rag technique at minute 3:26 here: