The name is pretty self-explanatory: a light-colored marking that would mostly cover the torso of the lion and then gradate along the limbs and head. It deviates a little from a literal Inverted Siamese because the paws and muzzle, in my mind, wouldn't be included. But it's up to Xylax if he would want to include them or not.

Just to show:

An example of Lilac Inverted Siamese with 100% opacity (markings over):


The marking doesn't have to be totally solid along the body, either. It could fade some like a regular siamese cat's pelt often does, letting the markings and base underneath show through.