New in Wolfram Mathematica 7: New Graphics Primitives  previous | next 
Use Vertex Colors for Interpolated Line Coloring
Use VertexColors with Line primitives to compactly describe interpolated coloring.
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Graphics3D[{CapForm[None], Thickness[.1], 

  Line[{{0, 0, 0}, {1, 1, 1}}, VertexColors -> {Red, Blue}]}]
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