Partial desaturation and other processes with a car

[Ofnuts]

From this:

   

To this:

   

One reason of the processing is the rather busy and uninteresting background (all buildings from the early 2000s) that distracts from the car.

Preprocessing:

• Straighten the picture using the measure tool, taking the corner of the building across the street as a reference (best take the reference near the center of the picture because it is not subject to perspective convergence, and anyway the facade of the building to the right isn't vertical...)
  
• Crop the picture to taste
  
• There is a large blue flower pot to the right that creates a nasty blue reflection on the fender. Fixed by sampling the car color, and painting over the pot reflection  in "Lch color" mode.
  

Then it goes like this:

   

• Make a path around the car (about 120 points)
  
• Make a path around the windows (everywhere they are transparent or reflect something)
  
• Using the windows path as a selection, copy/paste the windows on another layer
  
• Make a copy of the image and colorize it (Colors> Colorize). The color is picked to have a hue about 180° from the car color (car color is H=240°, so colorization uses H=60°)  
  
• Duplicate that colorize layer and  blur the copy
  
• Create a selection from the outline path (Path to selection), and subtract the windows path (Subtract from selection)
  
• On the initial image, create a layer mask and initialize it to the selection. You should end up with the car in original color over the "sharp" colorized layer
  
• Add a layer mask on the colorized layer, and make a gradient to go from  a sharp image in the front to a blurred background
  
• Adjust the opacity of the windows layer so that transparencies and reflections are between the original colors and the colorized background.