I've had do quite a few of these for clients and have found the trick to making the shadows and highlights look real is to realize that neither should have much color. I did this in RGB but it works equally well in CMYK.
What I'll do is start with a Solid Color layer set to the Color mode and at the color specified by the client. This will get me close but the shadows and highlights will have too much color.
I'll then use a curves layer to adjust the shadows–usually darken and pull out some of the color I just added. In this case I made the handles magenta so I pulled out some Red and Blue.
Next step is use a Hue/Sat layer to desaturate the highlights. I pull the saturation all the way back and use a mask to control what areas are effected.
For the masks I do the following. Command (Mac) or Control(Win) click on the RGB or CMYK composite layer. This will load the luminance data as a selection. I then save this selection as an alpha channel and name is Highlights. I'll then duplicate this alpha channel and invert it and call it Shadows. I'll then darken each with curves to taste. I just eyeball it, and will fine tune later if need be. I've attached the masks I used below.
I group all these layers together and then mask the group to the product since this makes tweaking the shadow and highlight masks much easier down the line. I'll usually make this mask with the pen tool and then convert to a selection. You can then adjust the edges with a brush if needed.
I'll also brush in a little of the color into the surrounding areas to account for light bounce to help the color integrate into the image better. In this image that's the shadows surrounding the knife bases and a little reflection on the knife directly left of the shears.