I see this was writen a year ago but my answer could save someone else a problem. The whiter parts are prone to burning in sunlight full stop, even in high humidity outdoors, most of these variagated Ficus were not meant for the garden either unless you can give them bright indrect light.
Another important problem to bear in mins beyond scortching but with similaer symptoms is a calcium problem. Growers of these for sale have the same calcium problem as we do but unfortunately we the consummer don't realise what it is and how to remedy the situation. Most Ficus are tricky to grow and produce for sale for the same reason. You have to keep up the calcium, ordinary 100% calcium carbonate will do the trick. If you dont symptoms much like these will start showing up but also making them much more light sensitive. Starting with new leaves inthis case you will get cupped shaped, distorted, stunted leaves (folding inwards or outward) often with necrotic edges (brown wilting or die back). With ordinary sunlight burn you get yellowing after the necrosis not with calcium shortage. With Clacium the browning crisp necrosis comes straight from dark green or whatever colour the distorted leaves are.
You need to apply water disolved Calcium carbinate untill the soil is alkaline rather than acidic. When planting in the garden this problem is less apparent as mineral soil is usualy rich enough in common micro ferts like calcium, though if planting in pure compost backfill you may have some micro shortage problems untill the roots can find their way out of it into real mineral soil. Leaf compost usualy has enough calcium if its very well rotted.
Potting soil used to grow Ficus at producers contains zero micro fert, it's usualy peat based or pure organic substitute so everything has to be given via watering including micros. Once you get it home these micro ferts are exausted almost straight away as a result, washed away with your first watering, unless slow release fertilisers with micro ferts has been mixed into the potting soil already. They will though eventualy run out and need replacing. The potting soil is prone to turn acidic instantly as the potting medium break down without micro ferts and this stops the uptake of calcium in it's track for Ficus even if the tap water is reasonably alkaline.
So I would try keeping it out of direct sun at all times indoors and give a ittle calcium just to be sure, it certainly will not harm it either but bear in mind it will take a few more stunted cupped shaped leaves before things revert to normal.
