i looked for the black seats in my car. to be honest given the cost of the dye, the time taken to do it right and my DIY ineptitude, the £100 or so the guy charged to touch in all the bits I wanted (handbrake cover, seat bolster, door card), it was worth it.
bmw offer this service by the way.
the seats are a bit shiny but mine seem to be anyway, no way near as matt as in the 435. must be an age thing.
last summer I seen a lot of owners form modified bmw owners club dyeing their seats using that leather die off ebay. You know what its like one person does it everyone follows. I was surprised by how good they turned out though almost like new you just keep adding coats until your happy. I seen pics of people literally just painting dye on with paint brushes. The one lad wanted rare cinnamon seats for his seca blue M3 so bought a grey set of spare seats and dyed them they looked perfect cinnamon brown to me. when fitted transformed the car. Seen others redo there's just to get rid of any lines/cracked marks and that worked too. Was quite surprised how easy and the results you get if my leathers ever get bad id re dye myself.
Thanks! It dries surprisingly quickly, even in winter, but I'd give it a couple of hours or so just in case. The handy thing about this method is that it isn't a huge immediate change, it gets better each use, so it's a lot harder to completely mess it up.