This would create a selection of the blue colors in the image.
Remix-a-Wallpaper
Description
This tutorial show you how you can redo/retouch a wallpaper which
someone else made but you want to add your own look to it. This is done
without the usual method of using the standard "Hue/Saturation"
image altering which completely reduces the image to a boring looking one color
scheme image. When your done our going to feel like a real remixer, like Puff
Daddy (P. Diddy).
Step 1
First pick the image your going to work with and as a note it helps if the
image has more than one base close color with a strong contrast between them.
The image I'm using is called "Focal point of my life" by
syragon, you can
download it here [link].
Now go to the the layer channel section and
click on the default blue channel in the layer channel section. Then while
holding the "Control" button on your keyboard, left click on the
thumbnail icon for the blue channel.
This would create a selection of the blue colors in the image.
Step 2
Now with the selection still active, go back to the layer tab and create a new
layer and fill with your pain bucket tool 
,
using the color=#FFC000. Finally set the "layer blending mode" to the
layer to "Hue" in your layer palette.
When your done, you should have something like this:
Step 3
Now that we have yellow in the mix, lets add some blue to the equation. Now go
to the channel tab and while holding the "Control" button on your
keyboard, left click on the default green green channel. With the selection
enabled, go back to the layer palette and create a new layer. Then fill the
selection with color=#526DB3, then set the layer blending mode to "Overlay",
this should give the image a bluish white gloss.
When your done, you should have something
like this:
Step 4
Now hide the yellow layer and leave the other layers visible. Go to the channel palette
and while holding the "Control" button on your keyboard, left click on
the default red channel. With the lection enabled, go back to the layer palette
and create a new layer below your yellow layer. Fill the selection with color=#A20000,
then set the layer blending mode to "Saturation", this should
give the red colors more emphasis.
When your done, you should have something
like this:
Comparison
Here is another example using a wallpaper called "4K"
by precurser, download it here [link].
Original:
Remix:
Additional tips:
- When creating the selection from one of the RGB (Red, Green, Blue) channels,
you can duplicate one of the channels you want to work with and adjust the
"Curve" or "Level" of the transparency by going "Image
> Adjust > Curve" or "Image > Adjust > Levels".
This would allow you to tighten the transparency of the color you want to select
or the darkness.
- When you've added your additional layers, adjust the order of the layers and see how they affect the look of the image, who knows, you just might find a more desired look.