What colour is this ?

T octopus

Just a bit unclear on what colour this is.

Calibrick

It's hard to tell from the picture, but it could be the "brittle blue" (a distorted LEGO color from an older brick) as discussed under a different color ID post. I generally just recycle those, as they cannot be matched in a regular build with other blue bricks.

From the lighting, it could almost be Medium Azure... so if you've ruled that out, it's that brittle blue potentially. :-)

Vosblokjes

It could be Maersk blue, it's hard to tell without comparison to known colors.

Pikka

To paraphrase doctor Gregory House: "It's never Maersk blue."
Medium azure, most probably.