I have a similar problem with iCal, and always have. It uses light grey on a white background for days and hours. Can't see the days well, but especially the hours, can't discriminate those at all. Am not sure why more people haven't complained, or why this hasn't been fixed before this.
Maybe it doesn't show up on iMac's which have their own monitors built in. I use a MacMini, with a Samsung monitor. Have played with the Samsung monitor's settings, but can't fix the problem that way either.
Did check my Contrast setting in System Prefs, and it's Normal, and all the way to the left.
I think Apple needs to fix this. I'm not sure there's anything the end user can do.
Outside monitors are not the problem. I have brand new MBP with high resolution 15" screen. It is beautiful. So the problem is not with a auxiliary monitor, it is an application problem.
Many people have complained about this dating back to 2006 at least. Apple seems to ignore this subject, when it ought to take 15 minuts to fix.
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