Thank you andresrcs. I do need to keep values in separate columns so your method seemed best. Unfortunately getting stuck on an error message.
colors <- c("Death" = "Blue", "Tamponade" = "Red", "Protamine" = "Orange")
ggplot(by_year_percentage, aes(x=arrivaldate)) +
geom_line(aes(y=deathpercentage), color = "Death", size = 1.5) +
geom_line(aes(y=tamponadepercentage), color = "Red", size = 1.5) +
geom_line(aes(y=protaminepercentage), color = "Orange", size = 1.5) +
labs(x="Year", y="(%)", color = "Legend") +
scale_color_manual(values = colors)
Getting the following error: Error in grDevices::col2rgb(colour, TRUE) : invalid color name 'Death'