If you compare a few game artworks and their game sprites, you'll notice that colors differ. It's usually shading though.
It may be due to the limited amount of colors in the games, or maybe it's Ken's coloring being off. But at times it's just odd, like Silver's eye color.
For an easy example, Silver's eyes in the intro are red while his artwork has it as gray, and his VS sprite has gray eyes for him. Almost every fanart I've seen has his eyes as red, and it would make sense since GF has a liking to making eyes and hair match, plus his concept art for gen 2 has him with red eyes.
Red is another example. His artwork has a grayish hue, but his sprite obviously is brown. Dawn is yet another example, where her artworks are both blue but leaning toward navy while almost everything else involving her or a counterpart is a brighter shade.
Which do you go by? The artwork or the games? Sugimori helps design some of the characters, so it makes sense he would know..