Ancient Stone vs Sun Ray

How close are they?

ΔE 15.1, loose: different enough that you should pick on purpose. Sun Ray is noticeably lighter, cooler than Ancient Stone.

Can I use Sun Ray instead of Ancient Stone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Sun Ray is noticeably lighter, cooler than Ancient Stone.

Can I use Ancient Stone instead of Sun Ray?

The same difference applies the other way round: Ancient Stone 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.