The names of the colors in Spanish must agree with the nouns in gender and number.
In Spanish the name of the color come after the noun they decribe, 
so, the form change depending on the number and gender of what is described.
Let see a list of some common colors and few examples:
amarillo       yellow
anaranjado -naranja     orange
marrón       brown
violeta       violet
rojo - colorado     red
rosa - rosado     pink
azul       blue
verde       green
gris       grey
blanco       white
negro       black
Watch this video showing you how to say the names of some colors in Spanish:
colores - audio
Compré una flor roja. I bought one red flower.
Compré dos flores rojas. I bought two red flowers.
Compré un sombrero rojo. I bought one red hat.
Compré dos sombreros rojos. I bought two red hats.
Tengo un auto negro. I have one black car.
Tengo dos autos negros. I have two black cars.
Tengo una cartera negra. I have one black handbag.
Tengo dos carteras negras. I have two black handbags.
It should be noted that in some areas the adjective anaranjado also is frequently used for "orange", colorado is used for "red" 
and rosado for "pink".
Usually a noun being used as an adjective (colors that come from names of things; chocolate (chocolat) ,esmeralda (emerald), 
mostaza (mustard), cereza (cherry), ciruela (plum), etc...) 
do not change form regardless of whether they are describing something that is singular or plural. 
They are called "invariable adjectives", but Spanish is a living language, so, a noun used in this way would be change when modify 
a plural noun and still be acceptable.
Un sombrero café. A brown hat.
Dos sombreros café. Two brown hats. 
Una cortina beige. A beige curtain.
Unas cortinas beige. Beige curtains.
Una media turquesa. A sock turquoise.
Unas medias turquesa. Turquoise socks.

page 1 of 2