when you say a color do you change the end according to if the words in the sentence are masculine or feminine? example: would white change from brancos to brancas if it is a feminine sentence? uma meia é branca um relogio é branco
Yes! But not all colors.
Colors that change:
Colors that don't change:
- Laranja/(no plural, see Davu's link)
- Violeta/(no plural, see Davu's link)
- Cinza/(no plural, see Davu's link)
- Rosa/(no plural, see Davu's link)
- Cor de abóbora/(no plural)
I believe laranja, cinza, violeta and rosa don't have plurals: http://lilinguaportuguesa.blogspot.co.uk/2010/04/nem-toda-cor-tem-plural.html
I guess that's because they are really "cor de xxx" just like your other example but have lost the prefix.
I'm not a native, but I believe this may be correct. If it is not, please write and I'll delete it. :)
When using colours in general, we should always prefer masculine. (As cores da minha casa são branco e preto. Branco é a cor.)
But when we say that one particular thing has the colour, then we should change the ending accordingly. (A casa é branca. As carteiras são vermelhas.)