Photoshop puts a vast arsenal at our disposal to fine tune our images. It seems that the better acquainted we become with it, the more we seek out subtle yet effective ways to enhance our work.

Blend Modes offer one of the most effective ways to fine tune the delicate intricacies for a desired result, and Photoshop boasts 27 of them. Two of the more popular modes are Color and Luminosity, which sound rather reminiscent of each other when in fact they are two very different things.

According to the Adobe blog, they are defined as following:

Color: Creates a result color with the luminance of the base color and the hue and saturation of the blend color.

Luminosity: Creates a result color with the hue and saturation of the base color and the luminance of the blend color.

To truly see the effect, open a new image and create a curves adjustment layer that is set to RGB with a normal blend mode. Apply a standard S-Curve and the adjustment will apply to both the colors and tonality of the entire image.
Set the blend-mode to color and it will only apply to the colors adjustments without impacting the tonality.

Set it to luminosity and the colors will stay very similar and only the tonality will be impacted.

Blake Rudis of f64 Academy further demonstrates the effectiveness of both color and luminosity modes in the following tutorial. He shows why people often prefer using the luminosity mode when working with curves and the color blend mode when working with gradient maps.

Getting to know the particulars of what each of these blend modes does in Photoshop and where they will best be utilized will ultimately improve your workflow.