Dark Reaper vs Cloud Sea

How close are they?

ΔE 17.5, loose: different enough that you should pick on purpose. Cloud Sea is noticeably lighter, more saturated, warmer than Dark Reaper.

Can I use Cloud Sea instead of Dark Reaper?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Cloud Sea is noticeably lighter, more saturated, warmer than Dark Reaper.

Can I use Dark Reaper instead of Cloud Sea?

The same difference applies the other way round: Dark Reaper is noticeably darker, 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.