Hey, I just wanted to give my rough translation of the 3rd page of the 2nd Monster Farm Report (https://www.mf-online.jp/lib_special.aspx) that addresses what color each food changes your monster:

Red: salmon, carrots, mushrooms, various meat, red food
Blue: (can't make out kanji), turnips, peppermint, blue food
Green: Green fruits, types of vegetables
Yellow: yellow fruit, (I think it says grain)
Purple: purple vegetables, fruits, pieces of meat

I'm sorry if this isn't incredibly clear, but I only had my kanji dictionary, the internet, and my year and a half of Japanese courses to work off of. I'm also interested in trying to decipher the next page that talks about food in relation to monster horn growth.

The first item in the Blue category is Crab.