Ok, so..

@Kenji Larsen had offered help, providing the missing text from the empty text file "0dfz7.txt", which, intentionally or unintentionally, got lost and wasn't retrievable. The text content of the file was:

pnlhcfpslerhzrgwpvyrvcspsxozrjwbeooakazviggsezhwihiheqgmtmlezwx

which was found to be a Vigenère Autokey chiffre text with the key

hint

and decodes to

ifyouarereadingthisyouaredoingitrightstoponeplustwoplusxisthree

"If you are reading this, you are doing it right."

"one plus two plus x is three"

So the chiffre contains a little helper text and the hint:

1 + 2 + x = 3

Your education system failed by definition if you don't feel the urge to.... gnnn arrr.. must..solve...

x = 3 - 2 - 1

This could be the missing hint to decrypting the FEZ code field from the waterfall image stego.

Reminder: There were some texts and haikus in the red and green channel, but not the blue one. Also, the channels were marked with numbers in the left upper corner, R=1, G=2, B=3

Together with the hint from the above chiffre, we can assume, that a hidden message (x) is revealed by subtracting channel 2 (G) and 1 (R) from channel 3 (B).

I had tried before to add and subtract various combinations of the channels by shifting the letters like in a Vigenère code, but without result. @Stuart Longland encouraged me to try it again, so here's the method:

1. translate the FEZ symbol fields of all three channels to three letter fields, whereas the ambivalent KQ simply translates to K and the UV to V.
2. map the letter fields to a number fields in the typical Vigenère style with A=0, B=1, ..., Z=25
3. generate a fourth number field by the rule (3*26 + blue - green - red)mod26 (whereas 26 is the alphabet length)
4. translate the fourth number field back into letters

I got this:

H, M, Y, L, K, F, Y, T, G, I, T, P, A, C, J, P, B, I, P, X, D, X, D, W, S, T, H, 
N, R, S, W, U, Y, K, U, O, M, G, P, N, G, T, P, U, H, S, Z, O, A, O, I, O, H, E, 
P, S, J, K, C, N, R, R, O, S, K, P, E, N, S, S, T, N, Y, K, T, N, T, Z, U, E, K, 
B, C, W, X, F, B, P, X, D, U, L, S, R, A, F, A, L, Q, W, K, A, E, Z, B, T, T, L, 
U, G, Q, O, M, H, K, W, L, R, G, Z, A, S, U, M, E, E, D, M, Q, A, H, M, H, E, O, 
Y, V, J, K, L, W, H, Q, U, E, S, W, M, S, N, H, E, Y, Y, G, E, L, O, Y, A, C, Z, 
Q, D, X, V, G, O, P, P, C, Y, Z, D, P, V, N, X, P, O, B, M, Q, H, U, U, L, O, M, 
M, X, S, N, W, U, Y, Y, K, O, R, A, L, M, Z, V, I, U, E, A, L, Q, Y, S, K, N, A, 
T, K, K, W, Z, D, O, V, Z, V, I, D, E, E, H, G, H, E, C, J, P, U, H, E, F, D, C, 
V, E, H, R, V, Y, W, M, V, A, D, R, A, W, O, Y, M, N, K, K, W, I, K, R, I, P, N, 
S, H, V, O, X, S, I, Z, P, G, D, U, L, H, D, B, I, J, S, A, R, D, Y, N, N, A, Z, 
X, N, H, Y, Y, A, B, W, C, L, L, G, L, E, M, N, N, O, D, Z, R, F, H, U, D, R, Q, 
F, U, S, X, Z, E, J, C, F, E, E, Y, T, R, U, X, D, Y, P, N, Q, R, N, M, A, T, F, 
N, R, X, P, S, L, V, G, Y, E, W, B, H, D, C, X, T, E, I, O, D, O, Y, E, W, U, T, 
B, F, X, C, K, J, V, C, Q, Z, A, K, E, T, H, M, H, D, V, V, S, M, D, Z, E, F, F, 
O, K, H, M, R, L, J, P, N, E, S, C, S, H, I, S, E, S, O, Y, L, A, N, M, C, Y, V, 
J, A, W, J, Z, W, E, S, Y, S, N, X, E, E, N, N, A, O, X, X, Q, F, R, M, S, O, J, 
G, R, F, P, L, X, B, H, T, R, U, F, P, R, F, G, L, R, Z, I, V, L, L, Y, H, U, W, 
P, Q, J, Q, M, Q, S, F, R, G, P, C, O, F, O, K, E, V, E, G, S, U, E, N, T, R, C, 
X, I, T, O, R, N, H, U, C, Y, E, R, S, I, R, Z, A, I, N, A, N, O, G, A, E, M, Q, 
M, P, U, W, Q, G, Z, S, G, P, A, K, T, S, M, Q, T, N, Y, F, O, T, B, M, Z, I, A, 
Q, E, I, Z, H, U, J, G, E, N, T, D, S, N, A, O, E, G, G, N, A, Z, L, E, M, S, Q, 
U, I, U, D, B, N, B, E, Z, D, X, G, C, O, T, Q, R, M, H, V, Q, J, P, I, X, S, M, 
G, Y, X, Q, P, I, Y, I, K, C, Z, Y, R, N, I, B, P, Z, M, G, K, W, C, S, T, I, N, 
Y, W, H, D, Q, Z, N, A, S, B, O, O, I, E, O, T, V, R, A, P, Y, X, R, Z, J, N, C, 
Q, F, L, D, K, Q, U, J, L, X, G, L, P, Z, N, Z, R, I, J, F, P, B, D, W, G, N, P, 
S, E, M, L, D, A, D, V, Q, N, O, X, T, W, H, M, P, D, U, N, J, N, X, H, S, I, D, 
J, Q, K, B, S, P, Y, B, M, N, T, J, Y, B, U, Q, U, C, X, W, K, O, G, J, K, T, Z, 
H, M, I, Z, P, Z, N, N, V, T, D, C, H, H, M, I, S, L, X, A, E, Q, N, O, U, A, D, 
I, X, I, D, C, E, I, G, L, E, D, Y, A, C, A, K, E, E, M, I, G, G, F, M, I, S, X, 
F, Y, L, O, Y, M, W, K, S, E, R, K, B, J, N, T, Z, M, F, O, J, Q, E, D, G, F, P, 
T, G, T, J, S, Q, O, U, F, X, L, X, E, J, S, R, Z, Z, F, Y, T, Z, R, T, C, O, C, 
S, B, Y, M, B, D, G, Q, B, T, V, N, N, Y, Y, Y, N, O, C, K, D, D, P, H, W, L, S, 
G, V, Y, U, J, E, T, H, P, V, U, P, O, I, L, Y, O, J, G, B, B, P, H, E, M, L, M, 
N, J, Y, L, G, W, D, W, Z, D, Q, B, D, W, Y, O, I, H, F, L, B, U, A, E, I, O, X, 
F, L, Y, E, E, K, F, Q, F, R, R, L, R, V, J, B, N, Y, T, Z, Y, K, H, R, O, X, C, 
N, I, H, B, C, K, K, K, D, T, E, G, U, A, V, M, Q, O, I, T, Y, P, H, S, S, S, P, 
M, S, T, I, P, R, U, N, X, J, Z, P, E, V, G, Z, J, P, B, O, G, E, V, W, B, F, U, 
V, H, L, P, B, J, B, C, R, T, C, X, R, K, A, K, M, T, N, Q, L, E, F, O, K, E, V, 
R, G, X, C, M, K, K, V, M, E, X, F, Z, A, V, L, Z, U, N, E, Q, M, W, O, N, B, M, 

And hey, even if it's not perfect, there's actually something in there:

So there are obviously flaws in the algorithm, but with a few more eyes on this I'm sure we can crack this!