If the object being described is feminine, then the color will be in feminine form. If the object is masculine, then the color is masculine. usually, objects that end in the feminine ta ة are feminine. For example, the word for car سيارة is feminine. So you would say السيارة لونها حمراء
on the other hand, the word for house بيت is masculine. So you would say البيت لونه أحمر
Transliteration of color names:
أحمر ahmar
حمراء hamraa
azraq / zarqaa
akhdar / khadraa
asfar / safraa
abyad / baidaa
aswad / saudaa
asmar / samraa