The only I can think of is spongebob, but he's not really human-like. If you can't think of yellow, can you think of other "wierd" colors like green, blue, red etc
The Smurfs, who basically led a human like existance despite being only 3 apples high and colored blue. The Snorks also had different skin colors as well.
As for ACTUAL humans, I think Doug's the only one beyond The Simpsons that goes for different skin tones.
The show's characters just had remarkably unique skin tones (Skeeter was blue, Roger was green, etc.). Whenever the show's creator Jim Jinkins was asked about this, he said it was his way of demonstrating that it doesn't matter what color a person's skin is - it's their personality that counts.
Well, a couple of Yellow-ish human-like characters that comes to mind are:
JLU's Android Amazo (after obtaining universal knowledge) transformed from silver grey to Golden yellow in color.
Another yellow-ish character was Brainthor, after the merging of Brainiac and Luthor, Brainthor had a Golden yellow torso, except for the head.
Sunni Gummy of 'Disney's Advs. of the Gummi Bears' and Butter Bear of 'The Wuzzles' are both yellow bear characters in their respective animated series.
Here's some yellow human-like characters that I can think of:
Pac-man had Pac-Man & Ms.Pac-Man were yellow ball-like characters who're not humanlike.
Classic TMNT had Screwloose who's a yellow human-like mosquito alien,if he counts.
Captain Planet had Duke Nukem who's a powerful radiation-loving yellow human-like monster(who's my favorite Eco-Villain).
Spongebob Squarepants had Spongebob & his cousin who're yellow nonhuman sponge people.
Xiaolin Showdown had Omi who's the best yellow main character.
JLU had the powerful android Amazo who transformed from silver grey to golden yellow.
Rave Master had Racas who's a weird, maracas wielding ring-hair styled yellow human-like demon villain of the Palace Guardians who's got awesome deflecting power.
Busou Renkin had Moonface who's the funny,silly-looking yellow moon man of the L.X.E. group of Dr.Butterfly's(who's my favorite villain).
Blue Dragon had Marumaro who's a funny little yellow human-like creature who's the girl-loving pervert of the day & comic relief as well.
Beet Excellion had a powerful yellow human-like Vandel during the end of the Harden battle.
FHFIFs had Cheese who's a funny yet annoying yellow imaginary friend who loves to annoy others for the fun of it.
Talks in an asian accent, the color of defining them like how a caucasian white and african is black, asian are refered to as yellow. Ever heard of the expression Banana or Twinkie before?