We generalize the operadic approach to algebraic quantum field theory [arXiv:1709.08657] to a broader class of field theories whose observables on a spacetime are algebras over any singlecolored operad. A novel feature of our framework is that it gives rise to adjunctions between different types of field theories. As an interesting example, we study an adjunction whose left adjoint describes the quantization of linear field theories. We also analyze homotopical properties of the linear quantization adjunction for chain complex valued field theories, which leads to a homotopically meaningful quantization prescription for linear gauge theories.Keywords: algebraic quantum field theory, locally covariant quantum field theory, colored operads, universal constructions, gauge theory, model categories MSC 2010: 81Txx, 18D50, 18G55 F (G)/(r 1 = r 2 ) (2.5) in Op C (M). Example 2.6. Consider for the moment M = Set. The associative operad As ∈ Op { * } (Set) is the single-colored operad (i.e. C = { * } is a singleton) presented by the following generators and relations: We define the set of generators of arity n by G(n) := {η} , for n = 0 , {µ} , for n = 2 , ∅ , else , (2.6) for all n ≥ 0. The generator µ in arity 2 is interpreted as a multiplication operation and the generator η in arity 0 as a unit element. To implement associativity and left/right unitality of these operations, we consider R(n) := {λ, ρ} , for n = 1 , {a} , for n = 3 , ∅ , else , (2.7)