I am unable to find the article talking about differences between Red and Yellow foots – I found it about 4 years ago when I got my yellow foots – It was talking about the differences between the species.

On your question about hybrids (Yellow and Red foots). I am no expert – but when did a Yellow foot have red legs?
http://market.kingsnake.com/detail.php?cat=50&de=572461

For those who have trouble telling the difference between Red and Yellow foot Tortoise have a look at this site
http://www.chelonia.org/articles/Gdenticulatacare.htm

The article outlines how to identify a Yellow Foot Tortoise.

My personal opinion is they are totally difference species.