but I'm not sure if this is how I would go about changing the color of vertical blinds. One of the professional painters on this site may have a different feeling about that, and they will advise you, BUT I would think that when you open and clos painted blinds, they will rub and clap together and eventually chip the paint. That would be really unsightly.
Have you considered re-applying fabric? It may be more tedious than painting, but should be more durable. Lay out each individual slat on a flat surface, apply a spray-mount adhesive, and apply a strip of fabric, smoothing it out the same as you would wallpaper with a smoothing tool or a brush. Cut away the excess from the edges and rehang. It would not only give you the color you want, but texture as well.