The color that a job has when it shows up on the calendar is determined by the language. This is set in the Administration/Maintain Languages screen. As you can see below, the example (Spanish) is set to display on the calendar in green..
The one exception to the color displayed is if the job is not assigned. It will always display in red until it is assigned and then it will revert to the language color as below.
The job showing above at noon today has not yet been assigned.
You will probably need to double check that you are not using red for any of your languages. Of course, you can still use red if you want to.