My opinion on the grayscale benchmark, although I never had a real problem in a competition with this :

Shaded
Ideal - K
Workable - C,D
Too dark - B,S
Impossible to see my writing : A

Thermo
Ideal - F
Workable - E,G
Too dark - H,I
Impossible to see my writing : J

Line
Ideal - M,Q
Workable - N,O
Too light/dark - L,P,R

Arrow
Ideal - U
Workable - T,V,X
Too dark - W


I think overall, I prefer lines (and arrows) darker than shading/thermo.
Also for clues (like coded), I'd rather they were small and in a corner rather than big and center (it also gives the advantage of printing them black instead of grey).

Thanks Bakpao, Veronika, TiiT, Kithyane for your inputs on the grayscale and others for their feedback.
More or less combining Ideal and Workable choices, it overlaps for all of you. We will take this into our consideration and implement these choices in the next round whenever applicable.

Thats a good point TiiT, it may be possible PDF rendering is impacting some way, hopefully not too much. We will see if there is any resolution setting that can be improved while generating pdf.

I'd say I'm in complete agreement with bakpao, would prefer as light as possible. (Saying this now because of Double Chocos on Puzzle Ramayan round that recently concluded. Shading of them felt so dark that I had trouble extracting solution codes.)