Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32h7rs/STM32H7R/LTDC/LTDC_L1CKCR#0x0
LTDC layer 1 color keying configuration register
color key blue value
color key green value
color key red value
https://github.com/modm-io/cmsis-svd-stm32