Touch, suggestion, suspicion, soupçon, tincture, tinge, shade, smack, spice, dash, vein, strain, streak are comparable when they mean a perceptible trace of something foreign, extraneous, or peculiar.
Touch can suggest an impression left on someone or something by or as if by contact with another, but in general it implies little more than an appreciable trace.
Suggestion implies an outward sign that is just enough to give one a hint or an inkling of the presence or existence of something.
Suspicion and soupçon differ little from suggestion , but they tend to imply a fainter trace requiring more delicate perception or evoking less certainty.
Tincture , tinge , and shade are terms used primarily in describing color.
Tincture and tinge usually imply an admixture with something that gives the thing affected a faint cast or an appearance suggestive of a lightly suffused coloring.
Shade implies enough of a trace to suggest the smallest possible degree of some quality; it usually derives its implications from the meaning of shade as a gradation in the darkening of a color.
Smack , spice , and dash are used primarily in relation to the stimulation of the sense of taste.
Smack suggests a trace which is pronounced enough or decided enough for one to savor it <the Saxon names of places, with the pleasant, wholesome smack of the soil in them —Arnold >
Spice and dash suggest a slight admixture or infusion, especially such as gives zest, relish, or pungency.
Vein , strain , and streak all suggest linearity and imply continuity though not necessarily evident continuity to the thing, usually a quality or condition, so designated.
Vein applies to a trace that runs through a personality, a work, or a movement in the manner of a vein so that it lies below or within the substance or character of the thing as a whole and occasionally shows on the surface or crops out.
Strain and streak can both denote a distinctive characteristic that runs through and modifies the whole of which it is a part.
They are used especially of a personal characteristic that is clearly distinguishable from or even contrasts sharply with the rest of one’s qualities.