I'm bored out of my mind, so here's an icon tutorial.
Go from
to

Okay, fix up your base. It's different for each picture, so I'm not going to list everything I did. Get something like this

Now duplicate the base and desaturate it. Set it on "overlay", 100%

Now, create a new layer and fill it with dark blue (I used #010c46). Set that layer to Subract (That's exclusion in PS, I think)

Our icon is nasty and yellow. So, duplicate the dark blue layer and set the duplicate to screen.

Create a new layer and fill it with a dark tan color (#cabea4) Set that layer to multiply.

Duplicate the tan layer and set the duplicate to saturation, at roughly 40%

Create another new layer and fill it with a washed-out blue (#849cb8). Set it to multiply

That's a bit too dark, so duplicate the desaturated layer and bring it to the top, setting it to screen at about 40-50%

Just for fun, let's add a text brush. I think credit for the brush I used goes to
myoosikal, but I could be wrong.

We need another new layer, this time filled with a tan color (#cda689) set to multiply

Now duplicate the desaturated layer and set it to screen, 40-50%, and you're done!

Other icons using the same technique:

Go from
to 
Okay, fix up your base. It's different for each picture, so I'm not going to list everything I did. Get something like this

Now duplicate the base and desaturate it. Set it on "overlay", 100%

Now, create a new layer and fill it with dark blue (I used #010c46). Set that layer to Subract (That's exclusion in PS, I think)

Our icon is nasty and yellow. So, duplicate the dark blue layer and set the duplicate to screen.

Create a new layer and fill it with a dark tan color (#cabea4) Set that layer to multiply.

Duplicate the tan layer and set the duplicate to saturation, at roughly 40%

Create another new layer and fill it with a washed-out blue (#849cb8). Set it to multiply

That's a bit too dark, so duplicate the desaturated layer and bring it to the top, setting it to screen at about 40-50%

Just for fun, let's add a text brush. I think credit for the brush I used goes to

We need another new layer, this time filled with a tan color (#cda689) set to multiply

Now duplicate the desaturated layer and set it to screen, 40-50%, and you're done!

Other icons using the same technique:

