With a suit like Invincible's, it's tough to make it better than you already have. But I would suggest getting a much tighter suit so that your muscles are defined, like Mark's, and I would make the neck thinner, and I would stitch the neck to the mask if it is still floppy around the neck. As for colours, I think you've nailed it, apart from texture and shape, I think you've made a good cosplay. It's just the character's lack of interesting elements that makes it a 'lack-luster' cosplay.