Instead of adding a legend manually and making sure the colors are consistent, use the 'Tag' property for each plot to separate them. Then use the function add_legend to add a legend. The function groups all plots based on their Tag property, and give each group a separate color. It uses the Tag property values as labels in the legend.
I have included the function varycolor by Daniel Helmick:
Added credit to Daniel Helmick
Inspired by: varycolor