ΔE 15.8, loose: different enough that you should pick on purpose. Amethyst Rayne is a little lighter, much more saturated than Terrestrial Titan.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Amethyst Rayne is a little lighter, much more saturated than Terrestrial Titan.
The same difference applies the other way round: Terrestrial Titan is a little darker, much more muted.
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 Amethyst Rayne on the colour wheel
All matches: Terrestrial Titan equivalents · Amethyst Rayne equivalents