IMAGE DUPLICATED TO CREATE BORDER

ORIGINAL IMAGE

Instructions for a PC. Instructions may vary slightly between Mac and Windows.

After opening your image in Photoshop duplicate the background layer. Right click on background layer>select the Duplicate Layer from drop down box.

From the Edit tab select Free Transform

Select and hold the alt-shift on any one of the handles circled in white.

While still holding the alt-shift keys drag the handle to center to make an equal sized border of your liking. Press enter or select the check mark above the image to apply.

Select the Background Layer to make it active. Select the Adjustment Layer icon found in the bottom of the Layers palette.

Select Hue & Saturation from the drop-down box.

With the Hues/Saturation layer active lower the Saturation & Increase Lightness.

Select the top layer to make it active. Then at the bottom of the layer palette select the 2nd style icon.

From the drop-down box select Blending Options.

Select the Stroke in the drop-down box. All the prior layer styles you have used will automatically show in the settings. I have left the size a little larger so it's easily seen but you can change it to your liking along with the opacity which I left at 100%.

Select Color. This will open up the Color Picker. There will be an eyedropper. (not showing in this screenshot but it will be there)  This will allow you to  select any color on the image for the stroke by clicking on that spot. When you are happy with the color select OK on the Color Picker.

You can select any, all or none of these Layer Styles. When you select any and make it active there are many adjustments you can make to each of them. All the adjustments you make will show on the screen so you can unselect or keep to your liking.
I've added a Bevel & Emboss for a point of reference. 

 When finished select OK.
Remember to Flatten Layers and do a Save As.
Please comment with any questions.  Or to just say you are gaining something from my post and I will continue creating more.