I know that it's something stupid but wouldn't it be usefull that the outcome-flow of a decision has a colored value? So instead of just showing 'false/true' on the flows showing a green colored true (or with a green background) and a red colored false.
I know that it's adviced so that the true-flow goes horizontal and the false-flow vertical but sometimes that is not ideal and in such cases a developer can make a mistakes and I guess that colored markings can prevent that.