Trollblood Base vs Faded P.R.U. Blue

How close are they?

ΔE 16.0, loose: different enough that you should pick on purpose. Faded P.R.U. Blue is a little darker, much more muted, cooler than Trollblood Base.

Can I use Faded P.R.U. Blue instead of Trollblood Base?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Faded P.R.U. Blue is a little darker, much more muted, cooler than Trollblood Base.

Can I use Trollblood Base instead of Faded P.R.U. Blue?

The same difference applies the other way round: Trollblood Base is a little lighter, much more saturated, warmer.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.