Calth Blue Clear vs Thunder Blue

How close are they?

ΔE 7.3, close: similar, with a visible difference side by side. Thunder Blue is a little lighter, more muted than Calth Blue Clear.

Can I use Thunder Blue instead of Calth Blue Clear?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Thunder Blue is a little lighter, more muted than Calth Blue Clear.

Can I use Calth Blue Clear instead of Thunder Blue?

The same difference applies the other way round: Calth Blue Clear is a little darker, more saturated.

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.