If your transfers are browning then this is an issue with Over-pressing.
Over-pressing can be caused by a couple of factors that will be detailed below.
Time: One of the most occurrences of over-pressing is too much time. Double check the time we suggest for that item.
Pressure: Too much pressure can place a lot of heat on to the surface of the item and cause it to scorch. If time and temperature are correct, try and reduce the pressure.
Temperature: If the temperature of the press is off and running hotter than it is currently reading then it will cause browning. To double check this we suggest using a IR Thermometer to get a better idea as to what your platen is actually heating to.