
Three different triangles fitting nicely together.  This one came directly out of the wonderful book 
Tilings and Patterns (p. 74).  There are a few ones similar to this one as well that I may put up there.  I'm more a fan of the patterns that come from polygon loops that are combined rather than ones like this. Still these ones are easily described since they have only one local neighbourhood.  The 
PolygonR&D program has only one subprogram that describes the path from a purple triangle it's neighbour.  The smallest triangles are not drawn since they are white.
tri {
  right
  scale 0.625
  left
  sides 3
  paint orange
  scale 1.6
  sides 3
  ifon none {
    paint purple
    3 { create tri
        left
    }
  } {}
}