Here's my first entry into this thread:

Here's the original:

Here's how I did it:
1) Crop & rotate 90 degrees
2) Levels adjustment layer
3) Curves adjustment layer to boost the blacks of the background and increase the whites in the smoke
4) Further Curves adjustment to increase the black area with selective masking of the smoke so that remained at the same brightness level.
5) Hue Saturation level to boost the colour of the smoke
6) New layer gradient filled with a colour gradient set to 'Overlay' mode so only the smoke colour was changed
There's a few more in my gallery. I particularly like the white ones, the only step differing from the above is after the crop and rotate, do a image/adjustments/inverse to change it to white background and dark smoke.

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