Cobalt blue...when I look a bit longer, yes there is some blue on the back.
I would say it is the sky reflection, the slimy was most definite black The shot was made in the late afternoon hours, the reason for using 1600 ASA.
Thanks beetleman,
I know what you mean. I have seen this black specie for the first time in Scandinavia. The most common European slug is brow, as far as I know.
The hole in the body could be the respiratory organ, really guessing here.