I have noticed that there is 2 add-ons in JIRA marketplace from same vendor (you) which does the same thing: add colors to statuses.
so which one should I use, "Rainbow" or "Resolution and Status Colors"? What is the difference?
Resolution & Status colors supports only colorize issues depending on Status and Resolution values. It check value of both fields. For example it first looks for resolution and if it is unresolved it looks for status field. It also handles closed status as a special case and allows you to use either resolution color or status color for closed issues. Rainbow does not have this status, resolution specific capability, but it can use nearly any single select field for coloring the issue.