Haven't confirmed this works better for 6300 but found this text on XDA
I made the bootimage with Adobe - Photoshop CS. Make a new 240x320 image. Convert it to 256 color with dightering than convert back to RGB. It is not neccessary, but the result is better for the 12 Bit display.
Save the picture in 16bit BMP format, with "flip row order" checked, and "R5 G6 B5" format in the advanced options. The final file size must be 153672 bytes !!
just a little detail, I think we don't need to enable the flip row order, my image is upside-down lol, going to test a little more, and there are 3 pixels, red, green and blue in one of the corners, also there's some kind of distortion, a list in the right side.
Using photoshop cs, edited my image, ctrl+t and flipped it vertically, saved it in BMP format, with flip row order enabled, and advanced->16 bit-R5 G6 B5 format, replaced the splash and flashed, result: image color correct, 3 pixels in the lower left corner(red green and blue) a barelly noticeable list in the left side of the image.