Edward Seago was a 20th century British landscape painter. Known in the US primarily for his plein air work in oil and watercolor. It’s hard to find books on his work but I have found some show catalogs of his plein air work. One book that can be found is
this “Edward Seago” by Ron Ranson.
He used a limited palette outside that varied from Indigo Blue, Ochre and Indian Red to different forms of primary colors. His paintings always had a great sense of color harmony, very expressive and spontaneous brush work thats shows only what is important to the painting. On the internet you can find galleries that carry his work and some will have catalogs.