I need help with this IQ test puzzle I found online

Question

_{This puzzle is part of the Monthly Topic Challenge #2: IQ Puzzle Parody}

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What's missing?

Hint 1 (for use after the first step):

There are three “types” of pixels. You should work through these three sets more or less linearly in some order.

Hint 2 (for use after the second step):

There are 24 slitherlinks.

Hint 3 (for use after the third step):

And?

Hint 4 (specification of hint 3):

What is used by all three?

Answer 1

Second Step

Following the clue from Auribouros's answer, if you take…

…every other pixel—that is, the pixels highlighted in red below:

…and then…

…brighten the image, or equivalently color white all pixels that are not pure black…

…you will get:

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Third Step

Combining the clues from the first two steps, take…

…the “white” pixels…

…and look at their…

…pixel values.

For example,

…the first grid has red values:

251 254 251 251 251
254 251   2 255 251
251 254 251 251 251
253 253 251 251 251
251 253 255 251 251

Now subtract…

…the larger values from 255. In the above example this yields:

4 1 4 4 4
1 4 2 0 4
4 1 4 4 4
2 2 4 4 4
4 2 0 4 4

Finally, remove the…

…cells equal to 4, e.g.:

. 1 . . .
1 . 2 0 .
. 1 . . .
2 2 . . .
. 2 0 . .

Which yields a…

Slitherlink puzzle with a unique solution:
(Image from https://www.dougandjean.com/slither/, which I used to solve all of the Slitherlinks in this puzzle.)

We do this once for each grid…

…and each color channel,

…filling in the…

…pixels corresponding to the edges used in the solution with colors corresponding to the color channel,

…which yields:

(Click on the above image to see its individual color channels.)

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Fourth Step

Thanks to doome for pointing out in their answer that if we take the…

…white pixels in the above image, their disjoint union fills the while checkerboard grid (except for one errant pixel.

So if we take the…

…pixels of the original image that we haven't used yet—which are the same checkerboard pattern—and multiply them by 255…

…we get:

(click on the image to see its color channels)

Then, if we take only the pixels that are…

…white in the slitherlink solutions, and combine them into one grid…

…we get:

(click on the image to see its color channels)

Which certainly looks like… something?

Answer 2

Potentially partial answer, but I think you're missing

this symbol

How do:

The removed squares correspond to numbers between 1 and 25, taking every number and converting it using A1Z26, we get the text HEXCOLOR, which might be missing an S at the end (square in the spoiler above)

Answer 3

Fourth Step

Following from 2012rcampion's answer, if you take…

…the resulting Slitherlink solutions for each grid, and isolate only those edges which are present in all three colors:

…we then see…

…that all the pixels are used once each, with the exception of just one. To see this, we overlay all of them below (using the 9th grid to demonstrate this):

Now, we look at the original image…

…and in particular, at the pixels we haven't used yet. We used the pixels in the "corners" of the grid to see the "SLTHRLNK" message, we used the "white" pixels to find the Slitherlink puzzles, but we haven't yet used the pixels lying on the "edges" of the Slitherlink.

On closer inspection…

…we find that these pixels are not all pure black. In fact, they have value 0 or 1 in each coordinate. We can increase the contrast of these pixels, as seen below:

(Click on the above image to see its individual color channels.)

Combining with the previous result…

…we can look at the RGB values of the missing location within each grid, getting the following values for each grid (reading the grids in the standard row-major order):
Grid: 1 2 3 4 5 6 7 8
R: 0 1 0 1 1 0 1 0
G: 0 0 1 1 1 0 0 1
B: 0 0 0 1 1 0 0 0

This is as far as I got.

I considered interpreting this several ways. Attempting to convert each color's string to ASCII gives Z9(cancel), which seems useless and incorrect. Alternatively, interpreting this as a color gives the color #5a3918, which is apparently called Irish Coffee, but I do not know how to use this either.

Answer 4

Following @Auribouros's partial answer, I took a look at each of the white squares.

I found cough 'several' cough pixel colors (I color coded them to make it easier to put in my revised image):

By the way, I got pretty desperate for colors at the end there. See Wikipedia's List of Colors in case you're confused about 'what the **** is cerise?'

Red: RGB(249, 246, 247), Hex f9f6f7
Green: RGB(255, 254, 251), Hex fffefb
Blue: RGB(251, 251, 251), Hex fbfbfb
Yellow: RGB(251, 254, 254), Hex fbfefe
Magenta: RGB(251, 253, 251), Hex fbfdfb
Cyan: RGB(251, 251, 253), Hex fbfbfd
Light-Gray: RGB(251, 255, 255), Hex fbffff
Dark-Gray: RGB(254, 251, 254), Hex fefbfe
Orange: RGB(251, 255, 251), Hex fbfffb
Brown: RGB(251, 253, 253), Hex fbfdfd
Light-Red: RGB(251, 251, 254), Hex fbfbfe
Light-Green: RGB(255, 251, 251), Hex fffbfb
Light-Blue: RGB(254, 252, 251), Hex fefcfb
Light-Yellow: RGB(251, 251, 252), Hex fbfbfc
Light-Magenta: RGB(251, 252, 252), Hex fbfcfc
Light-Cyan: RGB(252, 252, 251), Hex fcfcfb
Purple: RGB(251, 254, 251), Hex fbfefb
Beige: RGB(254, 251, 251), Hex fefbfb
Chartreuse: RGB(255, 251, 254), Hex fffbfe
Electric-blue: RGB(251, 251, 255), Hex fbfbff
Mauve: RGB(254, 251, 253), Hex fefbfd
Dark-red: RGB(251, 252, 253), Hex fbfcfd
Dark-green: RGB(251, 253, 254), Hex fbfdfe
Dark-blue: RGB(255, 252, 251), Hex fffcfb
Dark-yellow: RGB(254, 254, 254), Hex fefefe
Dark-magenta: RGB(253, 251, 251), Hex fdfbfb (separate from purple; slightly lighter)
Dark-cyan: RGB(255, 253, 251), Hex fffdfb
Pear: RGB(254, 251, 255), Hex fefbff
Orange-red: RGB(253, 253, 254), Hex fdfdfe
Silver: RGB(253, 251, 253), Hex fdfbfd
Desert sand: RGB(251, 252, 251), Hex fbfcfb
Cerise: RGB(253, 253, 251), Hex fdfdfb

So far I haven't finished coloring everything, but I have got this, which I plan to expand in the future: