So, I'm not gonna teach you guys how to color your manga icons with the brush tool, etc. There are plenty of different styles and tutorials that show how to do that. This is for once you've already colored your scan, how to brighten it up a bit. I wouldn't really suggest using this tutorial for any coloring style that uses a lot of screen layers because then it'll just end up looking too bright. Multiply layers are good.
So let's begin. :D
Take your manga scan, crop it, color it, yadda yadda, FLATTEN IMAGE. The newly flattened image will be the base, etc. Moving right along.
LAYER » NEW ADJUSTMENT LAYER » SELECTIVE COLOR
REDS » -100, 0, 0, 0
YELLOWS » -100, +100, +100, +100
CYANS » +100, -100, -100, +100
MAGENTAS » +100, +100, +100, +100
WHITES » +100, +100, +100, -24
Duplicate the Selective Color layer.
Duplicate the base layer, drag it to the top and set it to Lighten 100%.
LAYER » NEW FILL LAYER » #001E36 set to Exclusion 100%.
Set the Exclusion layer to invisible. Create a new layer between the Lighten layer and the Exclusion layer. Press CTRL » ALT » SHIFT » E, which creates a new merged layer. Set the Exclusion layer back to visible and drag the new merged layer to the top. Erase all the white background. This is also the part where you can add any sort of textures layers. Feel free to play with that.
AND YOU ARE DONE. :D
Other icons made using this technique: