Stormhost Silver vs Radiant Platinum

How close are they?

ΔE 16.7, loose: different enough that you should pick on purpose. Radiant Platinum is a little darker, more saturated than Stormhost Silver.

Can I use Radiant Platinum instead of Stormhost Silver?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Radiant Platinum is a little darker, more saturated than Stormhost Silver.

Can I use Stormhost Silver instead of Radiant Platinum?

The same difference applies the other way round: Stormhost Silver is a little lighter, more muted.

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.