Red and Blue

Migene Gonzalez-Wippler wrote The Complete Book of Amulets & Talismans. I asked her about the origin of the hexagram and here is what she wrote:

The hexagram or Star of David has been used in many historical, religious and occult contexts. Its origins are lost in the sands of time. In Hinduism it is a mandala symbol that has been found in Hindu temples built thousands of years ago. It represents the perfect state of balance between Man and God. But according to well-known scholar Gershom Sholem the Star of David can be traced to Aristotle, who used triangles in different positions to represent basic elements. This theory finds some support in the interesting fact that two of the three Hebrew letters in David's name are Daleth. In ancient times Daleth was written in a form that resembled a triangle. In Greek the letter Delta is also shaped like a triangle. So we have two triangles
(two Daleths or two Deltas) which are interlaced to represent balance out of chaos. That could be the Greek connection found by Professor Sholem. As you probably know the triangle that points upwards represents the fire element (color red) and the male principle in kabbalistic symbolism. The triangle that points downwards represents the water element (color blue) and the feminine principle. You must have seen some Star of David symbols where the upper triangle is red while the lower is blue. Tradition says that by balancing the opposite elements of fire and water in the hexagram David was able to unite the 12 Tribes of Israel. In Kabbalah the hexagram is associated with the sixth sphere of the Tree of Life (Tiphareth) that represents the sun.

Hexagrams have also been found in cosmological diagrams in other religions, such as Buddhism and Jainism. And, surprisingly enough, the hexagram can also be found in mosques and on other Islamic objects. The hexagram also appears in Solomon's fabled seal so that it could presumably have been known to him.

But it is also possible that because it is a simple geometric shape, like the square and the circle, the triangle may have been used in many ways, including the hexagram, by many different peoples across the ages.