ΔE 8.9, close: similar, with a visible difference side by side. Brilliant Blue is more muted, cooler than Sapphire Gem.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Brilliant Blue is more muted, cooler than Sapphire Gem.
The same difference applies the other way round: Sapphire Gem is more saturated, 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 Sapphire Gem on the colour wheel See Brilliant Blue on the colour wheel
All matches: Sapphire Gem equivalents · Brilliant Blue equivalents