Homer - Sloop Nassau
Whistler - Dutch coast
#1 Color wheel.
#2 Mixing complementary color mixing.
#3 Beth Herring. Beth found it challenging to keep colors transparent, and to get a great variety of colors.
She pointed out how different the colors look once they dry on the page. (They always dry pale.)
It is challenging to keep colors bright and still transparent. It takes practice to get the infinitely varying ratio of paint to water right. Try getting both bright and pale (more water) colors.
#4 Palette mixing. Get variations mixing neutral colors by varying 1, the mix of water and 2, the hue of the secondary color, in this case reddish orange to yellowish orange.