更改geom_smooth行中的颜色

Question

我想知道是否有人知道如何在geom_smooth行中使用不同的颜色，而不是选择用于绘制geom_points的颜色。

p3 <-
  ggplot(StemSoil, aes(DOYc, CO2, col = as.factor(Port), cex = 1)) +
  geom_point(na.rm = TRUE, size = 1) +
  geom_smooth(
    method = 'loess',
    span = 0.1,
    size = 1,
    na.rm = T,
    se = F
  ) +
  scale_color_manual(values = c("red", "steelblue3", "gray20")) +
  geom_hline(yintercept = 0,
             linetype = 2,
             size = 0.5) +
  #ggtitle("CO2 flux") +
  ylim(0, 20) +
  xlab("Date") +
  ylab(bquote('CO'[2] ~ 'flux  (' * mu ~ 'mol' ~ CO[2] ~ m ^ -2 ~ s ^ -1 *
                ')')) +
  theme_bw() + theme(panel.grid = element_blank()) +
  theme(
    legend.position = "none",
    axis.text.x = element_blank(),
    axis.title.x = element_blank(),
    axis.ticks.x = element_blank(),
    axis.title = element_text(size = 10),
    plot.margin = unit(c(-1.1, 1, 1, 1), "cm")
  )