Green tint when stacking RAW DNG images in Android

Question

I am trying to process multiple RAW DNG images by stacking them to produce 1 stacked RAW DNG image. First, I get the DNG pixel data into byte array, since DNG is digital negative, I then flipped the byte values using "~" and convert them into unsigned integer, now I calculate the average. With the average result, I flipped it back with "~" and save in "newData" byte array.

Below is the snippet on averaging 2 DNG images. The images are shot from OnePlus 3 in RAW (16MP DNG).

byte[] previousData //from previous DNG image

ByteBuffer rawByteBuffer = mImage.getPlanes()[0].getBuffer();
byte[] data = new byte[rawByteBuffer.remaining()];
rawByteBuffer.get(data); // from current DNG image
for(int i=0; i<data.length; i++){
    int currentInt = Byte.toUnsignedInt((byte) ~data[i]); 
    int previousInt = Byte.toUnsignedInt((byte) ~previousData[i]);
    int sumInt = currentInt + previousInt;
    int averageInt = sumInt/2;
    newData[i] = (byte) (~averageInt); // store average into newData
}
// save newData into storage in DNG format

However, the result image(link below) always show green tint on white color portion. Any ideas what went wrong in the process?

Here is the preview of the stacked DNG image

Here is the preview of original single DNG for reference