So, say you want to duplicate and use an exact color that you've seen somewhere and have it scanned in to your computer.....  

Taking this color data collection stuff a little bit further (see how I'm rounding out your education already?)...Once you have the sample points go to the Info palette and you can write down (how about the Notes tool) or open up your color picker right away and enter the exact RGB coordinates to get the exact color. (this works great for stuff you've seen in print mags or photos and ‘accidentally scanned in' but wanted to reproduce the same color).

Yes all these perrty colors still boils down to mathematical numbers, but this ensures you can get precisely the shade of color that you want (reproduced).

Just punch in the coordinates as shown.

Now you can do something like use that color that you just locked down on and create a new layer or background. Edit: Fill is one way of doing this. 

Do this onto a brand new layer please or you'll wipe out everything else on the current layer. The easiest way to ‘fill' is alt/opt backspace with your foreground color (which happens to be the custom color).

You can see our little color samplers are still in place and that we've filled a new layer with the custom color that we've chosen (haven't we?) from one of the samples. Now you know how to get an exact color and understand more about Photoshop.

To discover even more and in real-time video then get my Basic Photoshop training which is filled with over 8 hours of practical good shtuff.  It's the lowest price on the market for complete Photoshop training.