Hot answers tagged hdmi
Looks like you hit the bug https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1457369. It will be fixed in 3.19.0-20.20 which will be released the end of this week. If you can't wait, you can either downgrade your kernel or grab 3.19.0-20.20 from trusty-proposed (see https://wiki.ubuntu.com/Testing/EnableProposed)
Since you said that a screenshot shows normal colors, it is most likely a hardware problem. I would suggest testing on multiply machines to determine if its your machine's graphic card the cable or the monitor Though, I think it's the cable, try changing it.
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