Some highlight color from the cherry was picked up, and following the overlay guide, the brush tool at 20% opacity was used to add soft edge highlights to help create the cubed form. I like to use the brush tool at low opacity [about 10%] and build up the intensity in areas where a brighter highlight is needed...as on the upper forward corner.It gives more control and I think a more natural look to use multiple strokes instead of increased opacity.Since the light was coming from the upper right, the left side of the cherry needed to be in a bit of shadow. Picking up some of the darkest cherry color and using the brush tool at 50% a darker tone was added. Avoid getting it too opaque, allow some of the natural texture to show through. Always use colors from the object itself and not from the PS color palette. It creates a better match. If the proper density of color is not available from the object, pick up a color in the object close to it, make a swatch in the background, select it and darken or lighten it as needed for a source color. Most people would create a soft edged mask for this step. I didnt, I just brushed on the color and removed any part I didnt like with a soft edged eraser. I dont necessarily recommend this method, but I dont see the need to use a mask for every single procedure. Since this is on a separate layer I can still lighten, darken or adjust color without needing a mask. Just my quirk.Note: Getting the color right is the most important element in retouching and graphic arts. Your eye will pick up a minor color error much more quickly than it will notice a technical one.