Well his set design is his mutated form, so differences in his appearance there are to be expected. His armour colour could very well have changed from the mutation. His BS01 page does say his colour difference between Dark Destiny and Bionicle: World is an example of him rebuilding himself, but that needs a citation. I suppose it does makes sense though, given his initial role in the universe was to rebuild Matoran sent to him, so rebuilding himself doesn't seem out of the question.