This looks like some type of stress. More than one environmental / cultural stress can cause similar symptoms. For example, Avocado trees are very susceptible to excess soil moisture, which damages roots so they cannot function in proper water and nutrient uptake. Sometimes this results in wilting even though there may be plenty of water in the soil. Nutrient deficiencies can also show as different colors in leaves, however some Avos produce new growth that is more tender and sometimes of a different color; the leaf toughens and changes to dark green as it matures. For more help, you might like to take your photo to a local nursery, Master Gardener clinic or Cooperative Extension office. The more details you can supply as to the growing conditions, the better someone can assist you.