In reply to Philip Holland.

I'm glad you noticed that, too! I almost mentioned it in the post. The four colors that have "SeaGreen" in their names are interesting. SeaGreen appears darker than DarkSeaGreen and LightSeaGreen is a different shade altogether (almost turquoise). if you print the RGB colors, you get the following:

Name Hex R G B
DarkSeaGreen CX8FBC8F 143 188 143
LightSeaGreen CX20B2AA 32 178 170
MediumSeaGreen CX3CB371 60 179 113
SeaGreen CX2E8B57 46 139 87

I can't upload an image into a comment, but you can use an online color visualizer to see the palette yourself. From the RGB values, you can see that all the components of DarkSeaGreen are larger (=lighter) than the corresponding component of SeaGreen.

I do not know the history of how these colors got names. Who chose them and how? Presumably, someone typed the colors in my hand.