Answer
Criticality is determined as soon as a given factor (i.e. float, drift, or total float) is less than or equal to a given threshold (i.e. value). By default, the threshold is set at zero and the factor is set as float, meaning that as soon as an activity’s float equals zero, it will go critical. To override this setting, click and choose the Properties tab. Next to Criticality Threshold, change the value to something which allows activities to never go critical so as to over-ride their critical color (for example, -1000). Note: this will effectively ignore criticality across the entire schedule.
Another option is to use delay objects instead of activities. You may choose to override the critical color for all delay objects by choosing without affecting criticality for the rest of the schedule.