The pale leaves are more likely the result of low light, from winter and being indoors. You might be keeping it a bit too warm, maybe? Mine is happy outdoors and our nights have been going down into the 40deg.F (@ 4deg.C) range lately. Warmth would keep it growing but low light plus warmth would make the foliage pale like that. They need a little bit of a dormant period in winter. I would not worry, and certainly don't remove that nice big leaf unless it turns completely brown.
Those brown marks don't look like fungus to me either, but do keep your eye on them, and if they continue to go up the leaf, you could try sprinkling a little bit of cinnamon powder on the area. It is a mild fungicide and bactericide. Bugs don't like it much either.