"The pink pants are not mine."
Translation:I pantaloni rosa non sono i miei.
@rachmc: red, orange, yellow, green, (light) blue, turquoise, black, white, grey and brown are not minor while pink, purple, dark blue, silver, gold, bronze, jade, indigo and any irregular color like mahogany or vermillion are. So basically, the colors of the rainbow minus purple and plus turquoise, black, white, grey and brown are the only major colors in Italian that I know of. "Dark" (scuri), "colorful" (colorati) and "dyed" (tinti) also conform to the noun's number/gender.
For the possessive adjective, you always use the definite article (except for singular family members):
le mie sorelle
il mio cane
For the possessive pronoun, whether you use the definite article or not changes the meaning subtly:
"La gatta è la mia" means "The CAT (and not something else) is mine."
"La gatta è mia" means "The cat is MINE (and not someone else's)."
Except for unmodified family members, the definite article is required with the possessive adjective.
il mio zio alto
i miei pantaloni
The definite article is optional with the possessive pronoun, although using it vs not using it subtly changes the emphasis.
I pantaloni rosa non sono i miei. = The PINK PANTS (and not something else) are mine.
I pantaloni rosa non sono miei. = The pink pants are MINE (and not someone else's).
Some color names in Italian are invariable.