I've had both in the past, and have another jumbo young nigrita male growing up here now. The tendency for gaigeae to develop a higher gloss in most cases I believe is why they appear to have better colors to their irridescence... more black/purple/indigo color as you described, and it is pretty striking. A really nice Mexican Black can have a much better overall black saturation from what I've seen and if you get one of the nice shiny ones, I think they can look just as striking as any Black Milk, some even better just not quite as big. The underlying skin color on a Black Milk is in most cases also much lighter than a Mexican Black, sometimes giving them a less saturated appearance. You can see that noticeably lighter color in the bends of their body as they move and bend around. Also, not every one of them turn completely black and may show a hint of pattern somewhere. Cool to watch the ontogenetic change to black as they mature though, and you need to be ready to offer them a lot to eat... they eat like pigs, grow fast and get quite large as I am sure you already know. Their behavior is great also, very cool in that respect... very alert, active and pleasant to handle, not as much of a bite reflex out of the desire to eat everything in site as is the case with most nigrita. Nigrita don't really seem to care who it is that has ahold of them, if they are the least bit hungry they will have a nibble at ya. Especially males from my experience, and unlike everything else I raise, I have generally fed my male Mexican Blacks all they can eat and they still look for a place to get a taste of me.
Mike
