You cannot use custom fields to check another task's progress. the only option is through VBA code to refer to another task.

Using code you would need to loop through the list of tasks and set a flag if the task's predecessor is delayed -- however not available through custom fields.

However, if the task's predecessor is delayed and the tasks are linked, the successor tasks schedule should be altered. The start variance and/or finish variance shows any change from baseline. You certainly can set graphic indicators (Red, Amber, Green) using start or finish variance.

Julie