Dual Asus PA248Q Color Mismatch

Here is to hoping someone can help me out with this issue.

I have two identical Asus PA248Q monitors of the same brand and the colors don't match up at all. I sent the monitor that had the issue back to ASUS hoping they would fix it but it seems the problem is still there—despite them saying it was readjusted. I am assuming it is a Windows 7 problem but I can't say for sure.

The primary (left) monitor is about a year older than the second (right) monitor so I am thinking that could also be an issue but being that I sent back the problem monitor back for repair I am not sure anymore.

The problem I am experiencing is that they older monitor does not produce white the same way the newer second monitor does. The colors look richer on the newer monitor as opposed to the older. The primary monitor is plugged in using Display Port and the second monitor is plugged in using HDMI. I had done a cable swap yet the problem was still there. I even tried using DVI with no success.

I am considering buying a Color Calibrating tool but I am not sure if it will solve the problem. Has anyone had this issue and found a work around? I hope I explained myself well enough as it's difficult to write down the issue.

In a nutshell:
Monitor A is duller in color (white looks grayish)
Monitor B is richer in color (white looks white)

I read up somewhere that it could be the Video Card but I am still not too sure it that is the cause. I have an NVIDIA GeForce GTX 660. If anyone has any ideas I would be forever grateful.