Color every second task in CheckVist. Each sublist starts with the same color, i. e. the first and/or the last subtask might have the same color than the previous/following task one level up.

checkvist_alternating-color-of-tasks.css

/* set the background-color for every second task */
li.task:nth-of-type(2n+1) > div.coreDiv {
    background-color: darkgray;
}

li.task:nth-of-type(2n) > div.coreDiv {
    background-color: lightgray;
}

/* active selection should remain visible */
li.selectedTask > div.coreDiv {
    background-color: lightgoldenrodyellow !important;
}