Knight-Questor Flesh vs Burnt Sienna

How close are they?

ΔE 6.8, close: similar, with a visible difference side by side. Burnt Sienna is more saturated, warmer than Knight-Questor Flesh.

Can I use Burnt Sienna instead of Knight-Questor Flesh?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Burnt Sienna is more saturated, warmer than Knight-Questor Flesh.

Can I use Knight-Questor Flesh instead of Burnt Sienna?

The same difference applies the other way round: Knight-Questor Flesh is more muted, cooler.

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.