A method for preparing a polyol useful in the formation of an isocyanate casting resin or coating composition is presented involving the reaction of an essentially C18 fatty acid mixture with a monofunctional alcohol to form a fatty acid ester mixture, forming a epoxidized fatty acid ester mixture from the fatty acid ester mixture, and reacting the epoxidized mixture with an aliphatic alcohol to form a polyol. The polyol can be further reacted with an isocyanate to form a casting resin or coating composition. The fatty acid mixture contains at least 80 percent oleic acid. Polyols prepared by this method provide good color quality and improved color stability during storage when used in the production of isocyanate casting resins and coating compositions.