Red background means left hand file.
Yellow background means right hand file.
If SDKDiff was invoked as SDKDiff other_directory then red means the other_directory and yellow means the current directory.
White background means common to both files
Blue text means that the line is moved text
Black text means text that is the identical (white background) or different (coloured background).
Green text means that SDKDiff thinks that there is a corresponding similar line in the other file (see Zebra Stripes)