Not The Real Reason
A lot of people seem to think that a Smiley is yellow because it is such a warm color. This is true.
Yellow shines of optimism, enlightenment and happiness. Shades of golden yellow carry the promise of a positive future. Yellow will advance optimism and energy, as well as spark creative thoughts.
How does the yellow color affects us mentally and physically
* Mentally stimulating
* Stimulates the nervous system
* Enable the memory
* Encourages communication
True it applies to the smiley, but it's not the real reason
Stands Out. Not The Real Reason Part Two
Maybe he's yellow because he wants to stand out? This might be another good guess. However there are other ways of standing out in a crowd. He could be orange or florescent pink. He would defiantly stand out then.
Besides whatever color he was, he would stand out. You can't miss that big grin on his face. I often wonder what he knows that the rest of us don't.
The Real Reason
The real reason the Smiley is yellow has to do with anatomy. He is nothing but a big happy head. He has a mouth to drink with so he'll never be thirsty. With all the public appearances he must attend, I'm sure he drinks a lot of liquid.
Notice though, he has no body. He can still travel around by rolling to his next gig. However, I ask the question, how does he go to the bathroom? All that drinking and he can't go to the bathroom! He is yellow because he is full of urine. The poor guy might die from urine poisoning.
Speaking of no body parts to urinate, how does he reproduce? That part is need for reproduction. Unless he is a form of an Amoeba and just spits himself in half. That might explain why there are so many of them.