scale_color_manual 在 ggplot 中仅显示一种颜色

Question

我使用 RStudio 中的 ggplot 创建了包含一系列数据的折线图。我的图例仅显示一种颜色，始终是 geom_line 使用 show.legend=TRUE 的最后一种颜色。在这种情况下，图例中的颜色都是绿色。我缺少什么？代码如下：

ggplot()+
  geom_point(data = Q1Shipments, mapping = aes(x=Year, y=Shipments)) + geom_line(data = Q1Shipments, mapping = aes(x=Year, y=Shipments), color="blue", show.legend = TRUE) + 
  geom_point(data = Q2Shipments, mapping = aes(x=Year, y=Shipments)) + geom_line(data = Q2Shipments, mapping = aes(x=Year, y=Shipments), color="purple", show.legend = TRUE) + 
  geom_point(data = Q3Shipments, mapping = aes(x=Year, y=Shipments)) + geom_line(data = Q3Shipments, mapping = aes(x=Year, y=Shipments), color="orange", show.legend = TRUE) +
  geom_point(data = Q4Shipments, mapping = aes(x=Year, y=Shipments)) + geom_line(data = Q4Shipments, mapping = aes(x=Year, y=Shipments), color="green", show.legend = TRUE) +
  ylim(3500, 5000) + theme(axis.text.x = element_text(angle = 45, size = 15)) + 
  ggtitle("Shipments Per Quarter By Year") + theme(axis.title = element_text(size = 20)) + 
  theme(plot.title = element_text(size = 30)) + theme(axis.text.y = element_text(angle = 45, size = 15)) + 
  scale_color_manual(name="Quarters", breaks=c("Q1Shipments", "Q2Shipments", "Q3Shipments", "Q4Shipments"), values=c("Q1Shipments"="blue", "Q2Shipments"="purple", "Q3Shipments"="orange", "Q4Shipments"="green"))

在此处输入图像描述