I think it is Synsepalum dulcificum. Also called miracle berry.
The grey leaves in your plant may be due to carbon di oxide (deficit or excess I am not sure). In general miracle fruit plants need following conditions
1. Grows well at temperature 70 degree F. Plant will suffer if temperature is above 100 degree F or below 60 degree F.
2. Need atleast 60% relative humidity (grows well at 70 % RH)
3. Air replacement: Be sure that your air is replaced daily, or every other day to add needed CO2, and to prevent disease.
4. Miracle Fruit plant are very sensitive to salt or chlorine, so make sure that does not exist in the air.
what is miracle fruit tree? Please tell us what species it is. about 8 years ago.