A state appeals panel vacated an agreed judgment between a husband and wife — both Northwestern law professors — after finding “the entire agreed judgment was the product of fraud or collusion.”The 1st District Appellate Court’s Nov. 22 ruling was the latest turn in the heavily litigated distribution of the $3.5 million estate of Renata Black.Bernard S. Black, Renata’s son, persuaded a Colorado probate judge to appoint him as his sister Joanne’s conservator in December 2012, months …