The config file should be commented to explain what each setting does so they don't end up breaking the game.

To expand upon this, I'd also like to see a list of available options for the configs. So for example, the blocks themselves have options like drywall and flawless (there's another I cannot remember presently). I don't know what the options are for transparent blocks, would be nice to have the list somewhere :) (Doesn't necessarily have to be in the configs, perhaps a wiki page?)

If Your just interested in the options available I would suggest using the in game config GUI, it lets you swap between settings fairly easily in a nice easy to use manor.

I really would like to know what each setting does as well
I can't tell which setting affect what.

I also have wanted to know the same thing for quite awhile, so I did a little research and experimentation and here are my findings: (did not check every setting)

Client settings: information that is displayed when hovering over the block

Crafting: craftingoutput is how many flat colored blocks per block/dye used

Texture options: (I found almost all these options to do nothing)
Normal blocks: drywall, stone, wool, hardened_clay, noise, pulse, shimmering, flawless
Glowing blocks: drywall, stone, wool, hardened_clay, noise, pulse, shimmering, flawless
Transparent blocks: semi_glass, glass, noise_glass, flawless_glass

Now the fun part, I didn't research every option in these, so I'll just go over the ones that I did.

Hue: In the HSV model there's 360 possible hues, but even with huemax it won't go that high

These are the actual colors

I was going to use divisors of 360 but 120 wouldn't work (seems bugged) so I personally went with 150.
360 doesn't work either

Hue_max: the percentage of 360 hues which are allowed (high number)
Hue_min: the percentage of 360 hues which are allowed (low number)
Hue_range_exponent: didn't test
Hue_shades: the amount of hues which are actually displayed

Saturation: In the HSV model saturation is determined by a percentage, 1-100

These are how each color transitions from the color to white

Saturation_max: the percentage of 100 shades which are allowed (high number: hue)
Saturation_min: the percentage of 100 shades which are allowed (low number: white)
Saturation_range_exponent: didn't test
Saturation_shades: the amount of shades which are actually displayed, 1-100

Value: In the HSV model value is determined by a percentage, 1-100

These are how each color transitions from the color to black

Value_max: the percentage of 100 contrasts which are allowed (high number: hue)
Value_min: the percentage of 100 contrasts which are allowed (low number: black)
Value_range_exponent: didn't test
Value_shades: the amount of contrasts which are actually displayed, 1-100

Personally I set up my JEI so each hue takes up one page with all the values and saturations.
So 17 blocks across (value) and 26 blocks high (saturation) Here's a picture

also not totally sure I got everything perfect in this explananation

looks like same texture to me

Your picture looks like drywall for both,

Is what the two settings look like when I did the same test.

Textures does indeed do something it controls the texture of the blocks, by default "Drywall" theres slight inperfections, diffrent textures allow for diffrent looks. Flawless removes all imperfections. For instance STONE:

Exponent is used to adjust the curve of the shades/hues and such. higher exponents get more lower values ( closer to 0.0 ), fractional exponents tend to get more higher values ( closer to 1.0 )

I assume the "bugged" state of hue your describing is likely that FCB only supports 256 distinct hue values, I suppose that's something of an oversight on my part, since I didn't think anyone would use that many distinct shades, since most of them can't even be told apart.

Hopefully that answers any remaining questions anyone might have related to the settings.

yea for me actually every setting except stone and wool look like drywall
fcb 6.6
forge 14.23.4.2751
mc 1.12.2

Your changing/viewing the right blocks right? There is a setting for each type of block after all.

If you are I'm not sure why that would be the case. Its certainly working for me, and there have been no changes since 6.6.

I can't imagine why it would load those 3 textures and not the other ones. They just determine which file to load after all.