The reason I am doing this is because I had a boundary/border RGB(255,225,225) in the image. So, I converted the entire image (255,255,255) pixels to NoData. Now, here are my two issues:
1 - Even after setting the InputTransparentColor = FFFFFF in Geoserver as mentioned in the post Option2, the image border is not transparent. The border, got an ALPHA_BAND=0.0 surrounding the image. Instead of an ALPHA_BAND, I need a NaN value for the border. So, I need to completely remove the ALPHA_BAND and set the border to NaN.
2 - What could I do to convert to nodata only the RGB(255,255,255) image external pixels, without affecting the internal ones?