Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32u5/STM32U575/DMA2D/OCOLR_RGB565#0x0
output color register
Blue value in RGB565 mode
Green value in RGB565 mode
Red value in RGB565 mode
https://github.com/modm-io/cmsis-svd-stm32