There's no direct evidence I'm aware of that the Picts even had tattoos.

Caeser makes a brief reference to Britons dying their skin in his account of the Gallic wars. Later Roman writers variously interpreted this as referring to tattoos or body paint, Celts or Picts, green or blue colouring etc.

We think of woad as being blue, we even have the term 'woad blue', but it's possible to achieve a range of colours using woad mixed with other ingredients.

We have indirect evidence of what Pictish body art may have looked like, via things like their stone carving designs, but any comments on their body art, if they had it, are speculation.

The Pictish Tattoo: Origins of a Myth By Richard Dibon-Smith PDF paper

http://www.independent.co.uk/news/science/the-truth-about-the-picts-886098.html

http://www.needlesandsins.com/2014/03/tattoo-history-myths-exposed.html (this references my first citation only, but gives wider context about prevalent body art myths)