Characters who are physically disabled don't appear in games because the kind of things that characters do in games tend to involve a lot of physical activity. How's someone who can't walk going to be jumping over obstacles? How's someone who can't see going to be shooting things?
And your idea about dark skin is particularly ridiculous.
1) "Dark skin" is exactly worded, because if you were to say "non-white" it would be obvious that games made in Japan have Japanese characters, who are non-white.
2) At any rate, Japan has few black people and you would not expect to see any in Japanese games except as a percentage of the Westerner-type characters, who in turn are only a small portion of all the characters.
3) Street Fighter II contains a black character, an Indian character, and several non-Japanese Asians and it comes from 1991. I suppose "recently" means "within 23 years"?
4) A lot of games, especially games from before "recently", have characters who are not human and so can't be black. Exactly what race is Sonic the Hedgehog or the ship from Defender? A lot more games have characters drawn with such few pixels that you have no way to tell what race they are unless you say "that pixel has a brightness of under 50 so it's dark enough that the character is probably black".
Oh, and Constantine is based on a comic. Gabriel is white in the comic.