Unfortunately, you can't really tell the condition or protection abilities of the oil by its color. Only really way to check to see if the oil is OK - is to have it chemically tested via oil analysis.
Not really familiar with the Brazilian market 2012 Corolla XRS 2.0. The last time the XRS trim designation was last used was with our 10th gen Corollas - from model years 2009-2010 with the 2.4L 2AZ-FE engines w/5-speed automatics. So I'm not sure where the 50,000 mile/48 months came from - if it was in the factory service manual or dealership maintenance guide (I'd only believe the factory service manual one - should have a booklet with the maintenance quidlines come with the car). In the US models - it only recommends transaxle service at 60,000 mile/60 months if driven under "special operating conditions". It actually doesn't specify a transaxle fluid replacement until 120K miles/120 months.
That said - most of the transmission services are heavily dependant on driving conditions and driving style of the owner. The intervals indicated in the factory service manual are for most conditions. Some transaxles could actually be fine with the original transaxle fill for considerably longer than what the factory spec's - other cases, some need to change their fluids at very short intervals, do to excessive stop and go / towing, etc.
Also keep in mind that a service like this is not just to exchange the fluid, but to also remove any accumulated friction material during the break in process / covering the pan magnets. This is not visible from the dipstick - you have to drop the transaxle pan to really get it all out. The interval they give you should be read as whichever occurs first - time or mileage.
Can you wait to 50K miles before you change it and be OK - possibly.
Better question to ask yourself - if you do decide to wait until 50K miles (and roughly 77 months, given your rate of 31K miles @ 48 months) and something catastrophic happens to the transaxle that is directly related to an oil / lubrication failure - do you want to eat all the costs of replacing that transaxle yourself since you've pushed past the manufacturer's recommendation and it may not be covered under warranty (ie, abuse / neglect on owner's part)?
Note that it generally doesn't hurt you to replace fluids earlier - just that some owners want to maximize service interals and be more efficient with maintenance costs and old fluid disposal over the life of the car. If you look at the overall costs - doing a fluid exchange is pretty low in cost compared to cost to replace a transaxle. Like with most things on the car - potential damage from extending fluid intervals may not show up for many years, thousands of miles - if and when they come up, you definitely don't want the dealership to screw you out of warranty work because they looked at the maintenance logs and see that "missed" some fluid replacement and try to stick you with a huge repair bill.