Thank you mate for the kind words.
Firstly, they aren't quite as black as the indoor photo makes them look. But yes they are all darkened.
The problem with horns is this. When living, the keratin that makes up horn (and fingernail etc) essentially supplies it's own oil from within to keep them hydrated, unlike antler which is bone. This obviously ceases when they die and the horns will dry out and split if they are not treated in some way, and the cleaning/boiling process accelerates this. The most common way to achieve this is to use Linseed oil or similar. This will darken the horn unfortunately but will fade a little in time.
Personally I use a 50/50 mix of Linseed oil and turps, this helps penetrate better and leaves them less 'oily' but will still darken them to a degree. But the color in the horn is still there, unlike the fake 'black painted' look.
Cheers
Tim