Colorful literally means full of color, especially a lot of different bright colors. It can also be used in a figurative way to mean rich with interesting or vividly depicted elements, such as characters or events. Used as a synonym for the literal sense, vibrant means vivid, that is, strikingly bright or intense in color. Vibrant is related to the verb vibrate, a connection that makes more sense with some other meanings: vibrant can also describe things that are pulsating with vigor and energy (one might say vibrating), such as a vibrant city, and even personalities that are energetic and full of vitality. Use of the word vibrant to describe something that is brilliantly colorful suggests that the intensity and array of hues has an energizing or stimulating effect.
The adjective useful is commonly used to describe things that are in some way helpful or advantageous for a particular purpose: The recruiter provided the job seeker with a ton of useful information about the role. The synonym handy is a bit more informal and is used especially to talk about things that are convenient or that make things easier: The article was published alongside a handy glossary of terms so readers wouldn’t get lost in the technical terminology. Handy appears quite frequently in the phrase “come in handy,” as in, The article listed a bunch of tips and tricks that might one day come in handy.
When we describe someone as insensitive, we usually mean they are unfeeling or deficient in human sensibility, acuteness of feeling, or consideration: His glib remarks showed how insensitive he was. This descriptor implies a lack of awareness and responsiveness in thought and action. The synonym callous is more than just unaware or inconsiderate, it’s hardened to the point of cruelty. Callous means “unsympathetic” or “indifferent”: They have a callous attitude toward the sufferings of others. Its literal meaning is “made hard,” or “hardened,” as in the case of skin that has experienced repeated friction, resulting in a callus. Drawing on this earlier sense of the word, figurative uses of callous may imply that one is insensitive to hurt as the result of continued repression and indifference.