Difficulty: Quite easy if you're comfortable with masking
Translatable: as always, to programs with gradient maps :p
This type of technique will work best on caps that have something interesting going on in the background, and hopefully some details you can give a pretty color in the characters themselves (such as Margaery's dress).
The cap I used was this (originally from screencapped.net):
I can't find the fullsized version rn so let's just start with this already downscaled one - this was one of the icons where I actually start working on the coloring on a slightly larger canvas to get more details into the coloring, this would have been a very difficult icon to make in 100x100px so this is the size we'll start with.
Step 1: Duplicate the base, use Auto contrast (ctril + alt+ shift+L) and then auto levels (ctrl+shift+L) to give it more brightness.
Step 2: Usually I take the first few steps quite carefully, but with this icon I thought 'screw it, why wait to get crazy', so I made a pretty inanse curves layer:
RGB: O: 159, I: 102
Red: O: 189, I: 174
Green (3 points): O: 37 I: 45; O: 107 I: 99, O: 184 I: 163
Blue (3 points): O: 53 I: 77; O: 89 I: 143; O: 184 I:177
So basically something like this:
That weirdo shape was total experimenting, I had no plan whatsoever, and it led to this coloring:
Step 3: My icons just aren't complete without gradient maps, so make a gradient map with a light color in the middle and a saturated, darker color in the two ends, and set it on Soft light 40% (or something similar).
I (initially) wanted a yellow-blue contrast for the icon so I chose a gradient map like this:
Step 4: A copper gradient map on Soft Light 40%.
Step 5: Make a gradient map (YES, AGAIN .___. I'm practically married to them) of any colors you think would compliment what's already in the image. I really liked the soft beigeish browns and how they looked with the purplish/blue colors of the stairs and other background details, so I wanted to make those blueish colors more prominent. So, I made a gradient map from #f6dcc7 (yellowish/light peach) to #131159 (dark purplish blue), left it on Normal 100%.
Then give the gradient map a layer mask and mask away the characters (except for some details like Margaery's dress), and some parts of the background. It doesn't have to be super precise cause this image will be scaled down a lot so imperfections won't show much, I mean dear God look how clumsy my painting is xD
Step 6: Totally unnecassery step but I made a copymerge layer, used some Topaz on it (I don't remember the settings but I think I started with CrispStyle and lowered the accent setting down to 2 or so) and set the layer on Luminosity 30%. This doesn't do much but I thought it might improve the image quality a bit and make it less likely for parts to get grainy when scaled down.
Step 7: Make a copymerge layer, sharpen it (filter->sharpen->sharpen) and lower the opacity to 50% or so. It can be left a bit overly sharp cause the scaling down will make it much smoother. I don't know if it's better to sharpen before or after downscaling but I'd say before because some details might not even be there after the downscaling so sharpening them before might preserve them, idk?
Step 8: Now we're done with the large image! Make another copymerge layer, copy it, make a new 100x100px document and paste the large image on it. Resize and crop how you like, I chose a wide center crop that would show as much of the surroundings as possible.
Step 9: My plan was to pretty much stop once I'd resized it but it looked flatter and duller in this size than I thought, sooo I continued fiddling. This time make a gradient map from #290a59 (vibrant purple) to #ff7c00 (vibrant orange), actually I think this is one of Photoshop's default gradients, and set it on soft light 50%. This gives the icon some vibrancy and warmth.
Step 10: Next, I have a layer that's probably a blurred and desaturated texture so I have no idea who might have made the original one and what it looked like. Set it on hard light 100%.
I don't make many shiny icons, but when I do, I often prefer Hard light over soft light for the textures/gradients cause the effect is often smoother yet more dramatic.
Step 11: Make a Vibrance layer with Vibrance +100, leave it on Normal 100%. This is needed cause the lighting washed out the colors a bit.
Step 12: I like the new lighting and vibrancy, but I want the blueish tones and more detailed coloring back, so go back to the base (you know, the already colored sized down cap), copy it, bring it to the top and set it on Hue 100%.
Step 13: More texturing. Take this gorgeous light texture by midnight_road (it's one of my favorites, I've been using it on so many different icons when I want some vibrant, prominent light rays!).
I often smudge it a little to obscure that very bright, sharp part in the middle though (sometimes it works but in this icon it would break the 'soft' look).
Set it on Screen 100%.
Step 14: Next make a copymerge layer and manually blur some of the worst oversharpened parts - I usually use the Smudge tool rather than the Blur tool just because with the smudge tool you can smudge along the lines so the edges of stuff don't get all weird and super blurry but sort of create these new smooth lines instead. Ok that explanation made no sense at all but anyway, make sure you have the image zoomed in as much as possible (though not large enough to see only pixellated mess either) and the smudge tool as small as possible and with a pretty small strength setting (otherwise the smudging will get out of hand and the result is all smudgy. Which makes sense I guess but is not what I want here. I use 2px size and 20% strength).
So, I carefully smudged along Margaery's dress, the sharp lines of Joffrey's clothing, and some of the more pixellated parts of the background. Idk if it made any visible difference but doing this pleased my OCD.
Step 15: However now it looked a bit toooo blurred and underdefined to me so I copied the previous layer and used Unsharp mask with the settings 150%, 0.2px and 1.
Step 16: I wanted to make Margaery's dress stand out more and fit the more lit colors of the background better. So I just took a small round brush (I usually use 2px hard round brush for these things), and again zoomed in really really close and painted some highlights on her dress using a violet color picked from the background. I'm not much of a painter obviously and this effect could have been better if I had used multiple shades of that hue but I tried ok :D I set the layer on Screen 50%.
I could have stopped there but then I was like 'this is for margerydaw_s2 and she's a lighting master so let's make it even more lightingy'. I really don't know if this was a good choice at all, maaaaybe I overdid the lighting a bit but here we go anyway :D
I'm not exactly sure how I made this step cause I seem to have merged this layer away, it's missing from the PSD D: but I think I made another copymerge layer and used Filter->Disttort->Diffuse glow (it's good to have the default black and white as your currently selected foreground and background colors for this step, I really don't rememebr the settings though but just play around until you find a nice looking glow). I probably lowered the opacity of this layer to 50% or so.
Aaaannd we're done! Hope this was helpful! :> Just ask if some part wasn't clear, I explained some steps maybe a bit too hastily to avoid rambliness.