Data System Glow vs Mortarion Green Clear

How close are they?

ΔE 20.3, loose: different enough that you should pick on purpose. Mortarion Green Clear is noticeably darker, more muted than Data System Glow.

Can I use Mortarion Green Clear instead of Data System Glow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Mortarion Green Clear is noticeably darker, more muted than Data System Glow.

Can I use Data System Glow instead of Mortarion Green Clear?

The same difference applies the other way round: Data System Glow is noticeably lighter, more saturated.

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.