well.. since they are my favorite type of clowns and I've spent a small fortune collecting them in the pass three years.. I think I needa cue into this...
Though unlike the picasso and snowflake morphs which differentiate into classes by amount of whitening (which is still subjective on occasion). The onyx breed on the other hand has not receive the same attention and from my experience, extremely subjective.
One issue I'm bothered by is when black and white clowns (occellaris) is considered onyx (a certain extremely large fish store in OC do it all the time). IMHO, they're strictly True Perculas
The vague definition of onyx to my knowledge is an extra amount of blackening on the true perc's body... In that case, many hobbyist consider example 1 as an onyx.
If someone insist that example 1 is an onyx then so be it. There's no official definition or publication in a respected journal for me to debate and skew one's opinion to feel otherwise. Regardless of how flawed I feel theirs might be. hahaha..
What crosses the line for me to be considered onyx is connecting blackening between the clowns first and last line. Like this example..
I consider these guys 'high' grade onyx because their black coloring is almost entirely filled in. Extremely difficult to find wild caught like these. But in most cases, you'll find 'regular' onyx that aren't colored in entirely with black but does have connecting black inbetween the white lines...