Bright vs Dark
Likely the most widely used descriptive terms for timbre, they have a similar meaning in reference to sound as they do when they’re used to talk about visual color. Generally speaking, a Bright instrument will likely be more ear catching and intense. A Dark instrument (sometimes called Warm) by contrast will likely be more subtle and deep. Speaking technically, bright sounds are made up of more high frequency content, whereas dark sounds have more dominant mid and low frequencies.