Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32l4/STM32L4x6/DMA2D/BGPFCCR#0x0
background PFC control register
Color mode
CLUT Color mode
Start
CLUT size
Alpha mode
Alpha Inverted
Red Blue Swap
Alpha value
https://github.com/modm-io/cmsis-svd-stm32