ΔE 8.5, close: similar, with a visible difference side by side. Grey Blue is a little lighter, cooler than Terrestrial Titan.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Grey Blue is a little lighter, cooler than Terrestrial Titan.
The same difference applies the other way round: Terrestrial Titan is a little darker, 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.
See Terrestrial Titan on the colour wheel See Grey Blue on the colour wheel
All matches: Terrestrial Titan equivalents · Grey Blue equivalents