Remember I made this design prior to Manhunter's change of costume. So here are my thoughts about it:
As always I'd like to think logically when redesigning a character, what he looks should be connected to his background.
J'onn J'onnz design is pretty tough, which is also match by his background.
So I just went thinking of his other work as a detective"Manhunter" as the basis for the redesign. The good thing with Martian Manhunter is that he is not as iconic than the other characters. Aside from casual fans to hardcore fans, he is not that well known outside the community. So, there's more leeway in redesigning his costume.
The first thing I wanted to do with J'onn is clothed him. Because he is the other character aside from Wonder Woman who shows a lot of skin. Again that is something you can't take seriously. I gave him pants, what I learned from Ed McGinnis is to try to give some character to the costume, so in his pants the blue part resembles an M, which of course stands for Martian Manhunter. The red straps I made it bigger to cover more of his torso. The yellow parts I made it more organic, because I feel that the material is something related to J'onn's dna because when he shapeshifts the clothe changes as well, so I think everything he wears is organic. I didn't want him to wear a cape, that's why I gave him a stylize trench coat.
I'm not sure if the redesign is an improvement but that is my best attempt.
-access out, God speed
Read more about Martian Manhunter in my site here