There are three color (Blue, Orange & Green) indicators in JIRA. Issue tracking becomes easy with different color representation. These three colors are used to denote the amount of time spent on any particular issue.
Blue Color: Blue color denotes Original Estimate i.e., the estimated time to resolve an issue
Orange Color: Orange color denotes Remaining Estimate i.e., the remaining time to resolve an issue
Green Color: Green color denotes Time spent or Logged i.e., the total time spent to resolve the issue