I have a big, mature Shelob with 2 spikes.
One is fully established with 6 open flowers that don't look ready to wilt anytime soon. (There's some petal tip damage, but my fault from banging into it) The hard tan-colored thing in the middle is a stake, but to the left on the edges of the spike branches you can see some brown, particularly running up to the base of the flowers where it blends with the brown/maroon petals.
The other spike is brand new and about a foot long. It's growing so fast I swear it's got almost a new inch daily.
Sorry about the awful, awful lighting in here! That's not just a shadow, the fresh spike has some pretty extensive dark brown areas on it. They look to me like natural mottling of some kind, just coloration in the skin.
It's hard to tell from the pics if what you've got is similar, or if the spike is drying up instead.