Cinnabar, e.g. (3)
(Other definitions for ore that I've seen before include "Mined material" , "foreign money" , "14 [CURRENCY UNIT]" , "Mineral-bearing rock" , "it could be gold" .)
(Other definitions for red that I've seen before include "Inflamed" , "Colour for a blusher" , "'If you see it, perhaps you're angry (3)'" , "- - poker: Kniphofia" , "could be a Marxist" .)