I've had some of my pieces since 03, which isn't exactly a long time. But nothing has faded and I doubt it will. I would go on eBay and search vintage Speedy or something like that. You should be able to see that durability of the line.
Here is an example... still a beautiful leather, not dull or faded at all!
http://cgi.ebay.com/LOUIS-VUITTON-V...tem&pt=US_CSA_WH_Handbags&hash=item3f010e8380
I have a Mono that is 25yrs. and there is no fading.
I just love, love the monogram and never heard of it fading! You should defintely get it! What bag are you getting?