kniphofia said:Possibly sunburn.
DaisyI said:You could have two problems, too much sun too soon and under watering.
This plant was most likely grown in a nursery with shade cloth. Any amount of sun will burn it until it is used to more light. But new leaves should come out green and healthy as they developed in the new light conditions.
Are you watering enough? If its in a small Bonsai pot and your room is warm, it could need watering every day and as much as twice a day.