roseo-

from The Century Dictionary.

• noun In chem., a prefix used to distinguish a certain class of cobalt-ammine salts, which possess a characteristic rose-red color.

from the GNU version of the Collaborative International Dictionary of English.

• (Chem.) A prefix (also used adjectively) signifying rose-red; specifically used to designate certain rose-red compounds (called roseo-cobaltic compounds) of cobalt with ammonia. Cf. luteo-.