ΔE 13.3, fair: the same colour family, but not a straight swap. Royal Purple is noticeably darker than Terrestrial Titan.
✓ Two Thin Coats comparison chart lists these two as equivalents.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Royal Purple is noticeably darker than Terrestrial Titan.
The same difference applies the other way round: Terrestrial Titan is noticeably lighter.
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 Royal Purple on the colour wheel
All matches: Terrestrial Titan equivalents · Royal Purple equivalents