How to downgrade Color Depth from a template TouchGFX Designer project code?

So I bought STM32769 Discovery Kit and choose the TouchGFX Designer template accordingly and the default color depth is 16 bpp. So far so good, but then I want to examine the feasibility if I choose 8 bpp on this MCU, however the TouchGFX Designer under Config->Display->Color Depth does not allow me to choose other color depth. It seems the only way I can choose other color depth is by not choosing any template, but then I have to create manually the hardware init setting?

Anyone could please help me?