I am going to guess, guess being the key word here, that is a chronological issue. the III’s being not being around by the time the tri-color went into effect. Experts…What say you?
The ability and directive to apply camo over the new dark yellow base came out in early '43 and examples of this were first seen in large numbers during the Kursk Offensive in July of '43—mostly grren over the dark yellow, as it was summer. Actually, the greens were originally intended for spring/summer and the brown for fall/winter…however, during the summer of '44 it was fairly common the see both colors over the dark yellow base…less common was it to see just the brown over the base…I too have seen tri-color on some of the later Mk III variants…
The Herr Feldmarschall is correct of course! Also not uncommon to see late J/L tanks also sporting DY schemes if they were still in service (as many were) into mid-'43. And, to add to the possibilities, you also have Pz IIIs serving in Norway right up until the surrender in '45 that also had the 3-tone scheme even though they didn’t see any combat. [;)]