Whoah, certainly a biggun!
For the record, that's not a
mantis. It's a
phasmid or stick insect. Different order to the mantids.
I'd also have to check, but pretty sure it's not "girls are green, boys are brown" with mantids or phasmids. Colours would depend more on the species and even what instar (or stage of moulting) the insect is at. I know some mantids in first or second instars are black/dark, then as they mature they get lighter. Also check out the beautiful
orchid mantis which is neither green nor brown, but beautiful whites and pinks.