If I want a different color other than metallic gray, can I top coat Rust Bullet for Concrete and when should it be applied?

Yes, use the Rust Bullet top coats; BlackShell, WhiteShell, Color Shell’s or Clear Shot for a gloss colored finish. Apply the top coat when the last coat is dry to the touch; about 2-4 hours up to 12 hours. The previous coat should not be wet or tacky; if there is no transfer of coating to a gloved finger it is safe to apply an additional coat. After 12 hours, the surface must be lightly scuffed with 150 grit, to break the glaze of the coating. This 12 hour time frame is decreased in higher humidity areas.