the leaves are yellow with brown spots instead of a beautiful green... I also don't know what kind of orange tree it is :P
while i cant be of much help myself i found this link... http://www.ehow.com/list_7398069_causes-yellowing-leaves-orange-tree_.html Im very new to growing plants, but from everything I have read and seen it looks like a nutrient deficiency to me. Hopefully someone more knowledgable will be able to help and confirm my hypothesis.
If you don't get a satisfactory answer here, consider posting your question in Citrus Growers Forum where there are many enthusiasts.
