Iceflex has a glowing dark blue color. Mithral itself has a sparkling silverish-type, gun-metal coloration with elements of flakes and light in it, but iceflex has a more dull bluish hue, almost like ice crystals have embedded within, seeming to hold faint specks of light blue energy within. It is cold to the touch.
The Mighty Nein's Quest
"Manifold Morals" (2x74)
Ava Endlewood sells the party some mithral, but does not have any iceflex in stock. Umagorn melts the miscellaneous mithral into a single ingot, and tells them that it will change color when it is transformed by a white dragon's breath into iceflex.
"Rime and Reason" (2x75)
The party is successful in enticing Gelidon to breathe onto the mithral ingot, transforming it into the iceflex they need.
Returning to Uthodurn, the party escort Umagorn and Deilin to the Underforge where Umagorn successfully uses the iceflex to re-engrave Dwueth'var's runes and create a sword of silver metal with a slight blue shimmer to it, akin to the coloration of iceflex.