Updated documentation

examples/material/vertexcolor/vertexcolor.md

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+---
+title: Sprite Vertex Color Attribute
+brief: This example shows how to set and animate a vertex attribute
+scripts: vertexcolor.script, vertexcolor.vp, vertexcolor.fp
+---
+
+The `vertexcolor.script` sets the vertex attribute "mycolor", which has been specified in the material.
+
+![vertex attribute material](vertexcolor-material.png)
+
+The shaders specified by the material also makes use of the `mycolor` attribute to colorize the sprites.
+
+The vertex attributes can also be animated. Click the image for an animation effect.