Complex sentence: The key element to unify the look of the neighborhood was Welch's decision to repaint each of the houses in one of four colors, which he described as "sea-foam green, dirty flesh, butter, and dirty blue".
Split into simpler sentences: The key element to unify the look of the neighborhood was Welch's decision to repaint each of the houses in one of four colors. He described them as "sea-foam green, dirty flesh, butter, and dirty blue".