If I'm a girl do I say, "Mi color favorita es rosada." or "Mi color favorito es rosado."?
How does a girl say "My favorite color is pink." in Spanish? Is it, "Mi color favorito es rosado."? Or is it "Mi color favorita es rosada."?
Adjectives modify the noun that is the subject of the sentence. You are not the subject here, but the word "color" is the subject. "Color" is masculine, therefore, you'd use "rosado." If you used a feminine word, such as "casa," you'd then use "rosada."
When you are the subject of the sentence, then you'd change the adjective to match your gender. For example, a woman would say "Soy guapa" (I'm pretty) and a man would say "Soy guapo" (I'm handsome).
"Mi color favorito es rosado."
If you say "I am pink" (Estoy rosada), then you would use the female conjugation because it now becomes an adjective describing you.
Your gender does not affect the gender of the object. So it is "Mi color favorito es el rosado" whether a boy or a girl says it.
Note that the gender applies to "color", so it stays in the masculine even if you say: "Mi color favorito es el rosa", or "Mi color favorito es el rosita."
On the other hand, if you're talking about houses, for example, you would say: "Mi casa favorita es la rosada"