There is a website called Playr, it has Yellow along with Red, Blue, Silver, Gold, and Crystal(if memory serves). You can also play it on Vizzed.com. You'll need to make an account on each if you want to save your game.
I don't think that there is a current site that you can play Pokemon Yellow on, at least not legally.
You can play Pokemon orange online below but you have to download it.
You cannot play it online.
Go to Pokemon indigo online.
Yes it is 100% free.
if you want to play pokemon online they have a few on playr.org ex: pokemon crystal, pokemon soul silver and heartgold are on that site they are all old games theres also pokemon yellow, pokemon red, pokemon blue and pokemon green.On PlayR.Org
Yes you can play free on line
Pokemonindigo
There's no Pokemon Black game online. It requires download as in ROM.
playr.org, you can play pokemon games up to 2nd generation.
There is only one way. And it is to go to vizzed.com and download there emulator. Then you can play any game online free.
pokemonindigo.com