Translation:The colors of the flag are red and white.
I understand your explanation. However, it appears that the colours are tied to the word for flag, bandeira. A feminine words. So if colours are feminine, and the colours are colours in/on a feminine object, why do the colours not assume the feminino variations? Thanks :)
Thank you. I think I understand now. I hadn't been thinking of the colours as nouns. If the sentence had been "Vermelho e branco são as cores da bandeira", I would have probably automatically written the colours as masculine. Similarly, for "The shapes on the flag are circles and squares", it wouldn't have occurred to me to try to make the shapes agree with the word "shapes".