Dull Red vs Old Rose

How close are they?

ΔE 20.2, loose: different enough that you should pick on purpose. Old Rose is noticeably lighter, cooler than Dull Red.

Can I use Old Rose instead of Dull Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Old Rose is noticeably lighter, cooler than Dull Red.

Can I use Dull Red instead of Old Rose?

The same difference applies the other way round: Dull Red is noticeably darker, 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.