Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32f7/STM32F746/LTDC/L1DCCR#0x0
Layerx Default Color Configuration Register
Default Color Blue
Default Color Green
Default Color Red
Default Color Alpha
https://github.com/modm-io/cmsis-svd-stm32