Plonge leather is a fully aniline drum dyed lambskin. Only blemish free skins are dyed in this way & the result is an incredibly soft handle leather with rich colours.
In terms of a leather jacket, expect it to be very supple with a lustrous sheen. The leather is prone to marking more easily than say a regular calfskin jacket, but this often adds to it's patina.
Hope that answers it.