Magic the gathering booster pack?

hi peoples. i have a little probelem with booster packs in mtg. unlike booster packs theme decks tell you what colors are in side. on booster packs however it doesnt tell you the color or colors of that single pack. that is a probelm for me because if I was constucting lets say a green deck how would i know which packs i would need to get to complete my deck. or if i had a theme deck and wanted to expand to it and it was green how would i know which packs were green so i could expand to it