ΔE 6.7, close: similar, with a visible difference side by side. Transparent Red is a little lighter than Flag Red. They are different kinds of paint: Army Painter Flag Red is an opaque base/layer paint and Green Stuff World Transparent Red is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Transparent Red is a little lighter than Flag Red. They are different kinds of paint.
The same difference applies the other way round: Flag Red is a little darker.
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 Flag Red on the colour wheel See Transparent Red on the colour wheel
All matches: Flag Red equivalents · Transparent Red equivalents