Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32f4/STM32F429/LTDC/L1BFCR#0x0
Layerx Blending Factors Configuration Register
Blending Factor 2
Blending Factor 1
https://github.com/modm-io/cmsis-svd-stm32