I've recently noticed that in a few pictures I've seen, a person's skin tone is a Grey color. It's not really turned into black&white but it's not really color. How can I achieve this same effect?
Are you talking about selective colouring, where part of the image is black + white, while part remains in colour? (Click here for an example from an earlier post) If so, all you need to do is to desaturate part of the image, either by using the sponge tool, or by making a selection of the part you want to remove the colour from, then adjusting it to get the look you want.
You really have to post a link to said pictures. But I have a guess that your talking about duotone or tritone images. The quick and dirty way of duing this in photoshop is: Image-Mode-grayscale Image-Mode-8 bits Image-Mode-duotone Than load a preset ink ratio or make your own