It would make more sense (natively speaking) if it was "cărţile de colorat" (coloring books). Grammatically speaking it is correct to say "cărţile colorate" (colored books), depends on context. Albeit "cărţile colorate" will be seldom heard in daily life.
What is the rule about placing the possessive pronoun with respect to an adjective? In other words, why is it “cărțile noastre colorate” and not “cărțile colorate noastre?” “Cărțile colorate” seems like an unbreakable unity.