Link to a list of built-in colors (#99)

Author: areebg9

README.md

@@ -418,6 +418,8 @@ In order to display the plots in Jupyter notebook, we encode the image(which is
 |---------------------------------------------------|
 |cgColor: CGColor (return the corresponding CGColor)|
 
+Built-in Colors can be found [here](https://github.com/KarthikRIyer/swiftplot/blob/master/Sources/SwiftPlot/Color.swift).
+
 
 ### PlotLabel