Flag Colours
There are a lot of different colour codes you can use with the turtle.
Remember, to define a colour you use: color("goldenrod")
It doesn't seem to matter if you use capital letters for the colour name itself.
Colours A–D:
Colours D–L:
Colours L–P:
Colours P–Y:
There are other sources for sets of Python turtle colors available in various places on the internet. Try searching for "python turtle colors".