Red makes people feel powerful, alert. And red also means passion. For a president, he/she of course wants to make foreign people feel he/she is strong. However, the leader also wants to show his/her enthusiasm to the country. So red can show he/she is capable and full of zeal.
Blue makes people feel kind and peace. A president wear a blue tie when he makes a speech will make people think he is credible, and wear a blue tie on the election of president always makes people feel he/she is friendly and amiable.