Check your university's guidelines first
Many universities have official templates with set colors, logo and fonts for the title page. Check them before you design anything. If there are no rules, use a single accent color for headings and keep body text black or very dark gray.
Charts that work without color
Some committee members may read your thesis printed in black and white, or have some form of color blindness. Combine colors with different lightness and give each series its own labels, patterns or markers. The Okabe-Ito palette is a proven option for this.
Use the same palette in the document and the defense
If your charts use certain colors in the document, repeat them on your defense slides. That way the committee recognizes the figures and your work looks cohesive. For projection, increase the text size and check the contrast.