When two metals (or alloys) with differing electronegativity are in electrical contact within solution (or sweat) the metal with the lower electronegativity will oxidize. In the case of Gold (2.54) touching Silver (1.93), the silver will oxidize (tarnish).

In the case of a Silver (1.93) spoon sitting in an Aluminum (1.61) pan in water with a bit of lemon juice and/or vinegar and a pinch of salt, the aluminum (being 0.32 lower) will tarnish and the silver will actually un-tarnish! And if you are careful to make sure the only electrical contact between the spoon and pan is through a volt meter, you can even measure the 0.32 volts. Although not perfect (as it still needs to be buffed) this is a funky way to polish silver.

I bring all this up because Titanium with an relatively low electronegativity of 1.54, when in contact with Gold, Silver, or even Aluminum it is the Titanium that would oxidize. And since it it this same oxide coating that protects the Titanium, this is a win-win situation.

To belabor the point, Magnesium (1.31) with Titanium (1.54) would have the reverse effect. Where the Magnesium would oxidize and the Titanium would actually un-oxidize and you could loose or change the coloring effect.