Did you use any clearcoat or just the base color paint?

Isn't that's illegal?

Plus if you tinted the headlight... wouldn't you lose brightness of it as well?

It's not tinting the headlight lens, you're just painting the housing. It doesn't affect the light output at all.

It looks really nice in the first 3 pics, but then feels really blakc and dakr in the 4th. Which do you think is more accurate to how it really looks.

As others have mentioned- it's painting the actual inside of the housing. The 370z, as well as some other vehicles, have a true projector setup which does not need a reflective surface on the inside of the housing to direct light.

It's not illegal and the light output is great. :)