With Ofnuts plugin 'Decompose to color channels' I got quick a nice effect on a photo that was taken with a blue spotlicht in the back. Could be done with another workflow, but I found this a quick one.
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You can do the same with Levels/Curves and flattening out the Blue channel.
Things are a bit different if you just reduce the opacity of the Blue layer, the effect isn't the same as dimming the Blue in Levels.
If it's to remove blue, no plugin needed...
Just un-tick the visibility of the blue channel, or put down the blue curve of the right side
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or
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