(Exodus 16:31) "And it was like coriander seed, white ('gad')": I do not know (from this) what it was like. R. Yehoshua says: It was like coriander seed. (But then I would think:) Just as coriander seed is red, so, this. It is, therefore, written "white."
The Torah Gives You One Image, Coriander Seed, to Establish
Mekhilta Tractate Vayassa 6:7