after about 50.000 km the pigment of leather seat in my volvo V 50 lost from the laether. Some body can help me ?

I think that you would find that the leather in a V50 is not an analine or semi analine leather, but rather a corrected grain leather (if it is the same as my s40T5). The grain that you see in the leather isnt "real" - it is a print that is pressed into the leather, effectively in paint. An easy way to tell is to stretch a bit of the leather - if the grain is still prominent, it is probably corrected grain. Dirt and salt can be deposited on the coating from sweat and everyday use, and this can (because it is rubbed by the occupants) abrade the coating, hence color loss. This is why it is a good idea, even with corrected grain leathers, to clean them regularly (corrected grain can pretty much be done with soap and water, whereas analines need more care because they are porous). Then again, it might be something else entirely...

I sold my s40 with cream leather after all seats including the rarely used rear cracked leaving black marks on cream. All seats where replaced after many arguments one by one. I now, would not by a volvo with leather choosing the dalatech instead

Is "dalatech" the same as "delaro"? I have an '05 V50 with only 36K miles on it and already the "delaro" material on the driver seat is showing cracks. I live in Wisconsin, so the vehicle is certainly not exposed to extreme hot temperatures.

I have hardly got to that type of milleage (s40t5 15k miles). However my leather is still looking good.
Leather is an animal/naturale material. If not hydraded it will crack for sure over time. Extreme heat condition in a car can be quite damaging to leather as well.

I try to keep my car in the garage as often as I can. More importante I am using regularly Volvo care kit wich works great! Not only it seems to nurish the leather but it somewhat revives it to factory look unlike most of these very shiny looking aftermarket products.
I'm not the one to favor expensive dealer products but this one work really well.

Unfortunatly for you once the leather is cracked it will be hard to repair it.

Greg