The color and sheen of your vegetables can tell you a lot about how they will taste before you even take a bite. Lettuce that has gone from shiny to dull is probably going to seed, and will not taste good. The lower leaves on a lettuce plant may still be ok, but a rinse and pat drying followed by a few hours in the fridge may make them taste more like sweet spring greens.
But vegetable color can be deceptive too. A new cauliflower I have grown for a few years has made me realize how much I taste my food with my eyes. The orange cauliflower allows me to make cauliflower cheese soup with less cheese, because of the color it adds to the soup. The orange heads have more beta carotene, and are not genetically modified. No table vegetables are. But the extra cheese taste is all in my head.
I know people who don't like black, green, or yellow tomatoes-- even when they are fully ripe. The color is wrong. Do you prefer a beautiful tomato to a tasty one ?
Produce from your own garden or the farmers market may look different in color and shape than mass produced chemically grown vegetables. A hole in the lettuce leaf is a sign. This lettuce is so good even the insects like it. So don't discard or reject food that has a little damage or a different look- embrace it- cook with it - eat it.
While food appearance is part of eating, over reliance on looks can result in wasted produce, and will leave you missing out on many fine culinary experiences.
Go ahead- just try one bite.