Pull-tab and some key-wind cans included a plastic lid that could be used to reseal, or ‘reclose’ a can of tennis balls to keep the balls contained after use. The reclosure lid soon gained other uses such as displaying the manufacturer’s brand logo, and indicating the color of balls inside the sealed container. Sometime in the 1960s, Spalding introduced their Encore! balls with colored seams and the reclosure lid replicated the color of the new seam design.
Various reclosure lids. Note the blue, yellow, orange, and lighter blue Spalding Encore! lids in the upper left.