To ensure accessibility in touch-based GUIs:

1. Follow platform guidelines: Adhere to accessibility guidelines for iOS, Android, and other platforms.

2. Clear and simple layout: Use a consistent, intuitive layout and clear typography.

3. Large tap targets: Ensure buttons and interactive elements are large enough for fingers.

4. High contrast: Use sufficient color contrast between elements and background.

5. Closed captions and audio descriptions: Provide text alternatives for multimedia content.

6. Screen reader support: Ensure compatibility with screen readers for visually impaired users.

7. Font size adjustment: Allow users to adjust font size for readability.

8. Touch exploration: Enable users to explore the screen through touch without activating elements.

9. VoiceOver and TalkBack support: Implement support for built-in screen readers.

10. Testing: Conduct accessibility testing with real users and assistive technologies.

Additionally, consider:

- Colorblind-friendly design

- Reduced motion options

- Clear and consistent iconography

- Accessibility features like switch control or mouth-stick navigation

- Regular accessibility audits and updates

By incorporating these accessibility features, you can create a touch-based GUI that is usable by everyone, including people with disabilities.