Buy new slats to replace any broken ones. Clean the existing slats well with warm soapy water and dry them well. No matter what you do to create your own slat designs, you must start with an extremely clean foundation.
Cover the slats with new fabric to match your room decor. Use one of the slats as a pattern to cut a strip of fabric for each slat. Apply a thin, even coat of glue to a slat and carefully smooth the fabric strip onto the slat. Instead of glue, you can buy sheets of adhesive the same size as the slats. Regardless of the method of attaching the fabric, smooth out all the bubbles. If the fabric has a pattern, use care to match the pattern across the slats. Let the adhesive dry completely before reinstalling the slats onto the blind mechanism.
Paint the slats. Use spray paint or brush paint. Use specialized paints such as suede-textured or metallic flake for special effects. Paint a base color and stamp designs on the slats in a contrasting or complementary color. Use a sponge or rag to achieve other special effects. If the slats have a fabric finish to begin with, they will absorb a lot of paint, so buy more paint than you think you will need.
Dilute paint or dye with water and paint it onto the slats with a foam craft brush. The color will be translucent, so choose something that will coordinate with the base color of the slat and the colors in the rest of your room.