So I found myself in the hospital last night/this morning. And as all the nurses came in and out over the course of the evening I noticed that all had blue scrubs on. No surprise there really, until early this morning when one came in wearing scrubs with a orange patterned shirt. Immediately, I assumed that she was a "head" nurse or in some way more important that the others. Was she? I have no idea.
The point is there are times when we differentiate something with color intentionally, such as marking a value in a report red if it is negative. Most people know that difference in color is easily noticeable. For those book-smart types this would be known as a pre-attentive variable. Others are shape, texture, size and orientation. However, often times you see things in applications, on websites and in printed materials (or in Emergency Rooms) that may seem more important unintentionally.
So be careful when you choose colors for elements of your interface. We want users to think the important things are important; not the ones that happened to wear orange that day.