Hector Guerra asks when Linda changed from being white with green eyes to Asian
Better question: Why did she ever have green eyes?
Linda’s been asian since her first appearance back in #28, when William Messner-Loebs was writing the series, identified as Korean within a few issues (either right after that appearance or during the Celestial Enlightenment storyline, either way before issue #40).
Somewhere during the time Wieringo was doing the art, the colorists seem to have forgotten that asians tend to have brown eyes, and they went green for a while (maybe spillover from constantly correcting Wally’s eye color?), though they do fairly consistently color Linda’s skin a shade darker than Wally’s. Looking back at Terminal Velocity, I can see a definite change when Salvador Larocca started (though at the time, since I knew she was asian, I just interpreted any differences as variations in style, like comparing Wieringo’s Wally to Jackson Guice’s or George Perez’ Wally – although it’s not really fair to compare anyone to George Perez (except perhaps for Phil Jimenez)).
As far as the shape of her face goes, I’d chalk it up to varying art styles, but once you throw in the eye color, it makes me wonder if some bonehead editor wanted to downplay the interracial aspect of their relationship.