Google Sites Accessibility Guidelines
Make sure all your sites are accessible by considering these tips based on web standards and guidelines. Government and education websites especially need to comply with web3 content accessibility guidelines. Accessible and user friendly sites are also good goals for on-site SEO.
Add Image Alt Text
Unless your images are purely decorative and offer no relevant content, you should add alternate image text for screen readers. You can add alt text to all graphics on your site, including:
logo
header banner image
inserted page images
section background images
Here are instructions from Google Sites Help Center
View video tutorial for covering all the image alt options
High Contrast Text Content & Good Legibility
Google Sites will automatically adjust background images for readability. However, editors still have complete freedom with how they handle text color and whether they wish to cancel out the auto-adjust feature.
For legibility, basically don't go below 10px font size. In fact, 12px or 14px are a general standard for paragraph text.