Again from the internet:
the exxon encyclopedia says:
pale oil
straight naphthenic mineral oil, straw or pale yellow in color, used as a once-through lubricant and in the formulation of process oils.
the texaco/chevron dictionary/glossary says:
Pale Oil
A base or process oil refined until its color, by transmitted light, is straw to pale yellow.
Chevron/oronite says:
PALE OIL - straight naphthenic mineral oil, MVI to HVI, straw or pale yellow in color, used as a once-through lubricant and in the formulation of process oils