Orange = Tola'at Shani
Someone at Ledavid.com says that the Tola'at Shani, used in the Mishkan and Bigdei Kehuna was the color orange. Shani was also the color of the thread that Rahav tied on her window so the Israelite army would save her and her family. Immediately following this, the spies came to Yehoshua and said:
וַיֹּאמְרוּ, אֶל-יְהוֹשֻׁעַ, כִּי-נָתַן יְהוָה בְּיָדֵנוּ, אֶת-כָּל-הָאָרֶץ; וְגַם-נָמֹגוּ כָּל-יֹשְׁבֵי הָאָרֶץ, מִפָּנֵינוּ.
Based on this, the poster said that this is the reason why orange was chosen as the color that symbolizes the entirety of the Land of Israel.
I questioned that based on this Wikipedia entry, which seems to indicate that Shani is really red.
The poster replied that an Israeli researcher found out that Shani is really orange based on this article.
He also says that R' Hayim Vital, in Sha'ar Hakavanot, says that Tola'at Shani is red[dish], but represents the Hesed of Gevurah. The poster surmises that yellow is Hesed and red is Gevurah, so the combination is Hesed of Gevurah.