WCAG 2.1 Level AA · the standard ADA Title II names for public schools
Three tools: Check takes the colors from your slide deck, handout, or worksheet and tests every pairing, worst first, so the problems come to you. Find suggests new colors for the roles you have not filled yet, built around the ones you are keeping. Slides turns your colors into a one-slide PowerPoint template whose boxes are stacked in the order a screen reader should meet them.
Give one or two colors you are set on and say what each one is used for. Suggestions come for the roles you have not filled: body text needs 4.5:1 against the background, headings (large text) and accents (not text) need 3:1. + Add sends a suggestion to the Check tab, so the full pairing check can judge it with everything else.
Download a one-slide PowerPoint template whose boxes are already stacked in the order a screen reader should meet them — title furthest back (read first), footer at the front (read last). Screen readers follow the stacking order, not the visual layout, which is why most existing slides read in whatever order the boxes were drawn. The order here is fixed on purpose; it is the lesson. Works in PowerPoint, and Google Slides keeps the order on import.