From own experience, I know that OsO4 is colorless, but Cr2O3 is actually a solid green from what I have seen. but I guess it could appear yellow-greenish.
Answer is: OsO₄ (osmium tetroxide or osmium(VIII) oxide).
Osmium(VIII) is colourless, but most samples appear yellow, because of the presence of the impurity OsO₂ (osmium(IV) oxide), which is yellow-brown in colour.
Cr₂O₃ (chromium(III) oxide) is light to dark green compound. It is used as a pigment. In this chemical compound chromium has oxidation number +3.
It is called an amorphous solid because it lacks the ordered molecular structure of true solids, and yet its irregular structure is too rigid for it to qualify as a liquid.
