I'm using a KMR-1.8" display which uses a ST7735 driver and it is working ok with the Adafruit_ST7735 library. The problem is the display is very dim once the library has initialized.
If I reset the board, the last display buffer is still visible and gets about 3 times brighter until the driver initializes the ST7735 again. If I hold the reset down, the last display in the buffer remains on the screen 3 times brighter for as long as I hold down the button.
The LED brightness pin is tied directly to the 3.3v output of a voltage regulator.
My conclusion is that there must be something the driver sets that effects the brightness. I don't see anything that looks like a brightness setting in the spec. sheet or in the driver source code.
Update: I've systematically disabled all of the driver settings except the bare minimum and haven't been able to get the display to brighten up. I've even added commands to adjust the Gamma curve and it had minimal affect.
I've also breadboarded the display using a test rig and the display actually worked without issue on the breadboard, maintaining it brightness. This used the exact same register settings as the PCB version which dims.