# shade the term spread polygon(c(time(TB3MS), rev(time(TB3MS))), c(TB10YS, rev(TB3MS)), col = alpha("steelblue", alpha = 0.3), border = NA)
This code works well: tt <- if (!is.null(attr(Spread, "index"))) index(Spread) else time(Spread) y10 <- as.numeric(TB10YS) y3 <- as.numeric(TB3MS)
polygon( x = c(tt, rev(tt)), y = c(y10, rev(y3)), col = alpha("steelblue", 0.3), border = NA )