If your vinyl blinds have been around since the last century but you would rather not replace them entirely, update them with paint. While you could paint them with a brush, spray paint ensures a more uniform look, free from brush strokes. Make sure the blinds are completely clean before painting them, otherwise the paint may not adhere properly.
Clean Those Blinds
Wipe both sides of the blinds down with a duster or blind-cleaning tool. Close the blinds completely in one direction; wipe them down, and open and close them again so the blinds face the other way, wiping them down again. Add a few squirts of a mild dish soap to a bucket of warm water, along with a few caps full of white vinegar. Swish the water around with a sponge, and then wring the sponge out to wipe down one side of the blinds. Open and re-close the blinds so they face the other way, wiping them down once again with the sponge. Clean the plastic handle that controls opening and closing the blinds as well if you plan to paint it -- or even if not. Allow the blinds to dry completely.
Preparing for Paint
Take the blinds down from the window and find a place -- ideally outdoors, or at least in a well-ventilated space -- where you can hang them using loops of fishing line. A swingset or even a taut clothesline are possible hanging places. If you have no place to hang them, set a plastic tarp on the ground and place the blinds on the tarp, extending them so they're in their largest or longest shape so you can paint each slat with ease. Close the blinds in one direction most of the way, allowing a tiny gap between each slat so the paint spray covers one full side of each slat.
Painting the Vinyl
Select a spray paint specifically designed for plastic, resin and vinyl, otherwise the paint won't adhere properly. No primer is required for some plastic spray paints; otherwise feel free to use a plastic primer along with a standard spray paint. Shake the spray can for a minute or two. Then spray the blinds, beginning and ending each paint burst beyond the edge of the blinds to help prevent drips. Once the paint dries, apply another coat if necessary, allowing it to dry as well. Paint the horizontal bar that holds the blinds up as well. Flip the blinds over once the paint dries, and then adjust the angle of the blinds as needed to paint the other sides of the slats.