Complex sentence: The distinction between "warm" and "cool" colors has been important since at least the late 18th century but is generally not remarked in modern color science or colorimetry in reference to painting, but is still used in design practices today.
Split into simpler sentences: The distinction between "warm" and "cool" colors has been important since at least the late 18th century. It is generally not remarked in modern color science or colorimetry in reference to painting, but is still used in design practices today.