Plants with a red color are poisonous. Some plants that are red are poisonous, but not all. The point is there is no one rule to aid in identifying poisonous plants. You must make an effort to learn as much about them as possible. It is to your benefit to learn as much about plants as possible.
Many poisonous plants look like their edible relatives or like other edible plants.
For example, poison hemlock appears very similar to wild carrot. Certain plants are safe to eat in certain seasons or stages of growth and poisonous in other stages. For example, the leaves of the pokeweed are edible when it first starts to grow, but it soon becomes poisonous. You can eat some plants and their fruits only when they are ripe. For example, the ripe fruit of mayapple is edible, but all other parts and the green fruit are poisonous.