Its actually the blood vessels! Their blood vessels run directly beneath their skin, which is thinner than marine dolphins. So they appear pink, its actually just their blood!
They also have some pink pigmentation, which helps.
They also blush like humans do, when we are nervous or exited, our hearts beat faster, and the blood vessels swell in our faces, and the dolphins do it too when they are happy or exited.
You have mentioned albinism, and its pretty common in these dolphins, although it can be hard to tell which are true albinos, as they can be brown, pink, grey and white. And the albinos are pinky/white.
The dolphins who live in clearer water are more grey, because they loose some of their pigmentation, but ones in muddy water are far more pink/brown, as it helps them camouflage.
They are amazing creatures aren't they!