Mercury Mariner V-250 V-275 Outboard Service Shop Manual 1990, Page 232Get this manual
4 Note the color of gear lubricantWhite or cream color indicates presence of water in lubricantCheck drain pan for water separation from lubricantPresence of water in gear lubricant indicates the need for disassembly, and inspection of oil seals, seal surfaces, 0rings and gear housing componentsGear lubricant which has been drained from gearcases recently operated may have yellowish tint appearanceThis is due to agitationaerationDO NOT mistake this for water contamination