The pale referred to in the idiom is usually taken to mean the English Pale, the part of Ireland under English rule, and therefore, as perceived by its rulers, within the bounds of civilization. pale see: beyond the pale
For the food, see Salmon as food. The chum salmon (Oncorhynchus keta) is a species of anadromous fish in the salmon family. It is a Pacific salmon, and may also be known as dog salmon or keta salmon, and is often marketed under the name silverbrite salmon.
Therefore, by a number of properties the first place belongs to keta's caviar, which is orange with a glimpse of red. Next goes light orange caviar of pink salmon and caviar of red salmon with almost maroon large grains; such caviar is especially popular in Europe, while here keta's caviar is preferred.