Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32l4+/STM32L4P5/LTCD/L2CLUTWR#0x0
LTDC Layerx CLUT Write Register
Blue value
Green value
Red value
CLUT Address
https://github.com/modm-io/cmsis-svd-stm32