Concerning the letters behind FIYTA Model number, 
your guess is right! 
The detailed meaning is as following;

First letter : Means Case Color
Second letter: Means Dial Color
Third letter : Means Band Color
Forth Letter : Means Special Material

W- white (or no plating), B- black, H-grey, 

G-golden, R-red, Y-silvery, L-blue, T-two tone, 

N-green, T (only the forth letter)- Tritium tube.

The first Two English letters 
before the model number:
G- Man style, L- woman style, A- Automatic watch



For example,

GA8040WBWT:
It's a Man style automatic watch 
with steel white case, 

black dial, white steel band 

and tritium tube hands and markers. 

L226TWT (no "A" after "L" 
means it's a quartz watch)
It's a Woman style quartz watch 

with two-tone case and band, white dial.

more help and F&Q coming soon . . .