Is there a software for OS-X that will do all those tasks? Finding screen-coordinates (x,y), the pixel color below pointer, and distance between 2 points?
You can show screen coordinates if you start taking a screenshot by pressing ⇧⌘4:
You can also use it to measure the width and height of areas:
To abuse bundled applications even further, it's easy to get the diagonal in AppleScript Editor:
You can see the color of pixels with DigitalColor Meter: