Rather useful and decidedly fun!

I downloaded and used in almost a single step, and want to recommend this app to everyone the least bit scientific.
My first use of Colorimeter is finding equi-luminescent colours to use as an adjunct to reading a book titled Vision and Art: The Biology of Seeing (Margaret Livingston), to gain an understanding of certain visual effects used in art.
I intend using this app as part of my ongoing effort as a photographer to see colour more accurately. Different blacks, for example.
I have asked about the feasibility of an adjustable-diameter sample circle (in separate email). So far, everything else is there for me.

Sure, the price of the app is relatively high, not being an app aimed at the popular market, but worth it unless your down and out, and I want to tip my wallet in the direction of the apps author(s) in thanks.

PS. Quadriminds colorPicker is a good companion app (its free), inasmuch as it lets the user sample from a stored image as well as running live like Colorimeter. The other is limited to RGB, but also takes photos. I have not compared the two for consistency.

PPS. Colorimeter definitely does need bright sunlight for accuracy.

HousMouse about Colorimeter - Digital Color Picker, v1.2.2