Fenrisian Grey vs Sky Blue

How close are they?

ΔE 16.4, loose: different enough that you should pick on purpose. Sky Blue is a little lighter, more saturated, cooler than Fenrisian Grey.

Can I use Sky Blue instead of Fenrisian Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Sky Blue is a little lighter, more saturated, cooler than Fenrisian Grey.

Can I use Fenrisian Grey instead of Sky Blue?

The same difference applies the other way round: Fenrisian Grey is a little darker, more muted, 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.