How do I know when I can delete /edit the color appoints on my iPhone 6 calendar app?

[iMore Question]

iPhone 6 calendar app editing

I can edit/delete the "blue" highlighted appointments but I cannot edit/delete the "orange" highlighted appointments. What determines the color and how can I delete / edit the orange ones?

 

[kch50428]

Re: iPhone 6 calendar app editing

iCloud - Calendar & Reminders - Apple Support