Welcome to the HP Forums. I would be happy to help you with your HP Officejet Pro 6830. I understand that your printer is not printing in blue color and you have already done some preliminary troubleshooting.
Don't worry though as I have a few steps to determine the issue and find a solution as well,
Check the paper.
Check the print settings.
Check the estimated ink levels.
Print and evaluate a diagnostic page.
Make sure that the cartridges are properly vented and seated correctly.
Click here and follow troubleshooting steps mentioned in the document to fix this issue.
If these steps does not work, I request you to contact HP Phone support for further assistance on this.
Let me know if that works.
Sandytechy20 I am an HP Employee
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