Plausible, credible, believable, colorable, specious are comparable when they mean capable of impressing the observer, auditor, or reader as truly or genuinely possessing the quality or character that is set forth or claimed.
A thing or sometimes a person is plausible that is capable of winning acceptance, approval, or belief by its or his apparent possession of qualities which make it or him seem pleasing, genuine, or reasonable at first sight or hearing; the word need not definitely imply a false outside, or an intention to deceive, or a lack of soundness, but it usually connotes such a possibility, even though it also clearly suggests an ingratiating or mentally satisfying character.
A thing or less often a person is credible that seems to be worthy of belief or of being credited, sometimes because of plausibility, but more often because of its or his support by known facts or by sound reasoning.
A thing that is credible because it comes within the range of possibility or probability, or because it is in accordance with other facts that are known, is believable.
A thing is colorable which at least on its face or outwardly seems true, just, or valid or which is capable to some extent of being sustained or justified.
A thing or, less often, a person is specious that is outwardly or apparently attractive, beautiful, valid, or sincere but that is inwardly or actually the reverse in character. Specious is the only one of these terms that clearly implies dissimulation or fraud or deceit or hypocrisy.