"should" doesn't come into it. If you cook from dried at home, they will be a washed-out pale green/yellow/pale brown. If you buy canned, it will depend on whether colour additives (typically riboflavin and Brilliant Blue FCF) have been used. If you don't want the "interesting" bright green colour (and the word is fluorescent, with a "u") then look at the label and choose those with no added colour.