Hope you will enjoy following tool which I made in my spare time. It's running now only on Windows platform but soon I will publish it for OSX as well:
catEYE is a pixel picker and color meter which analysis the master screen display of Windows and OSX platforms. Color at different positions can be evaluated in multiple patch mode. It is also possible to track color along a given straight line from the screen in line mode. It is based on CIE-L*a*b, CIE-L*C*H, L+SH, YCbCr, YCH (Rec709) evaluation methods. Color Space data is shown in two dimension as Waveform Monitor and Vectorscope.
You will find it at www.m2port.com