The HX8872C allows 10-bit gamma correction. The datasheet provides default values for 2.2 gamma, but you can adjust registers 0xE0 (positive gamma) and 0xE1 (negative gamma) to fine-tune contrast.
A common reason for display failure is an incorrect software initialization sequence. The HX8872C datasheet provides a flowchart. Here is the recommended order: hx8872c datasheet
writeCommand(0x36); writeData(0x48); // Normal RGB scan direction The HX8872C allows 10-bit gamma correction