First off you will need to copy an image of smoke from google and copy it to GIMP. After that open GIMP and select Gradient. You want the first full saturation.
Then make a new layer.
Then select that tool from the side (Sorry i forget the name so just refer to the picture)
Then make a line through the the middle and do it as straight as possible.
You should now have a rainbow over the picture. Then go to the side, right click on New Layer, and Add layer mask.
When it says Add a Mask to The Layer, select black and then add.
You will then be back at the smoke image. Click on the paintbrush tool.
Then select the brush shown. I forget the name but i believe it is called fuzzy brush 19.
Then color all over! and make sure the gradient is still set to the first Full Saturation. Then when it is all colored i like to tap the brush over every area to make it look better. and that's the end! :3
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