I opened the repeated neighbours sudoku for today. I got stuck after a while and realized that there is perhaps an error in the sudoku. If you look at the grid element in the 8th column and 6th row it is obvious that R6C9 and R7C8 should be the same, which, in effect, means that the 4 on R7C9 should be yellow too. But it is not. I am surprised that one person has solved it too.