Hard to tell the real color; because it is completely infected with citrus rust; cut it open and see what it looks like inside. The leaf looks like a lemon

Citrus rust?! Is that why the fruit is brownish outside?! Wow i thought that was just the look of it. I'd love to begin caring for this tree if its curable. I noticed it has mealy bugs and a nutrient deficiency but didnt know about the rust. Heres the fruit...idk if its ripe but it has a pleasant taste to me...Mildly sweet but more tart than sweet actually