This set is called ´The Little Golden Book Library´. It is a four volume set in the colors you described in a sleeve . It was widely advertised for sale in little golden books and the golden magazine. I would suggest you look on ebay. Go to the first page of this site and click on the logo to register.It has appeared there from time to time. Check each week.Good luck!
I am looking for a set of four books (1 blue, 1 green, 1 red/pink, 1 orange) that are compilations of Little Golden Books. They include around 15 each of complete Little Golden stories (The Saggy Baggy Elephant, Scuppers, etc..). My mother bought a set for my older brother in 1971 or ´72 for Christmas from a book club. My younger brother and I would each also like a set of these books, but we are unable to find them anywhere. If anyone knows what I´m talking about and where I can find them, please help me!