Explanation
Correct answer: A.
Choice A is the best answer. The convention being tested is the use of verb forms within a sentence. A main clause requires a finite (tensed) verb to perform the action of the subject (in this case, "yellow"), and this choice supplies the present tense verb "is considered" to indicate that yellow is considered a complementary color to blue in modern color theory.
Why the other choices are wrong
Choice B
Choice B is incorrect because it results in an ungrammatical sentence. The nonfinite participle "having been considered" doesn’t supply the main clause with a finite verb.
Choice C
Choice C is incorrect because it results in an ungrammatical sentence. The nonfinite to-infinitive "to be considered" doesn’t supply the main clause with a finite verb.
Choice D
Choice D is incorrect because it results in an ungrammatical sentence. The nonfinite participle "being considered" doesn’t supply the main clause with a finite verb.