Elements or rooms highlighted in red indicate that an error has been detected on the plan. These errors can be of various types: collisions between two elements, non-compliance with regulations, missing or misplaced elements, etc.
Any red element on the plan is associated with an alert visible on your error detector. You can consult this detector to get more information and correct your plan accordingly.
For example, here there are only two high outlets in the kitchen, whereas the NFC 15-100 standard requires a minimum of three high outlets.
When you click on an error in the detector, the affected element or room turns blue on the plan. This helps you quickly locate and identify the error.