Limax cinereoniger is a big land slug in the family Limacidae.
I found this one underside the mushroom in the wood in Moravia, Czech Republic:
Although it is thought to be the longest land slug species, it is shrinked like this:
It seemed a bit pale and especially the foot was very pale. I have taken it and taken no photo of the foot. It has great color variability, but the mantle is unicolor always and the sole has three color parts always.
I have taken photos of the same specimen 26 days later. It grow up and the three color parts of the foot are visible more clearly:
Horsák M., Juřičková L. & Picka J. 2013: Měkkýši České a Slovenské republiky. Molluscs of the Czech and Slovak Republics. Kabourek, Zlín, 264 pp. (in Czech and English). page 115.