I felt in love with the way this graphic designer, called Mariusz, has edited this picture.
It would be fun to produce something like this for myself.
Anyone has some ideas on how to create such a nice color effect in Photoshop or Gimp?
Starting with the source image in greyscale:
Add a layer with a gradient fill on top of it, adjust the blending mode for the layer to something that looks nice. I chose Soft Light and tweaked the opacity.
These are the steps I took using GIMP to create a color gradient on the source image.
Choose the Blend tool to fill with a color gradient.
Create a new gradient with desired colors (Left HSV 21,83,91, Right HSV 301,52,60)
Apply the Blend tool in Mode - Overlay along a line from left to right:
Blend mode Color for a stronger effect: