Choose an appropriate preposition to fill in the blanks:

He was indifferent____success, painting not for the sake of fame or monetary award, but for the sheer love of art.

The preposition 'to' is used with the adjective 'indifferent', forming the phrase 'indifferent to', which means not caring about or not being interested in something. Therefore, 'to' is the correct preposition to use in this context.