API: Apply vertex color

Mel has the polyColorPerVertex command, that will change the color of one vertex at a time. This works fine you're doing it on less than 100 verts at a time. But on more than 1000, it really starts to slow down.

Enter the API. The MFnMesh class has a setVertexColors method which allows you to set multiple colors at once. And it is much faster.

Pseudo code to use it:

import maya.OpenMaya as om

# Build an empty vertex ID array:
idArray = om.MIntArray()
# Now fill it with the vert ID's on the object to color.
# Could be some, or all of them.

# Build an empty color array:
colorArray = om.MColorArray()
# Now fill it with the colors for each of the vert ID's 
# defined above.

# Get a MDagPath for the object we're coloring:
selList = om.MSelectionList()
selList.add(myObject)
mDagPath = om.MDagPath()
selList.getDagPath(0, mDagPath)

# Get a MFnMesh for our object:
mFnMesh = om.MFnMesh(mDagPath)

# Apply the colors:
mFnMesh.setVertexColors(colorArray, idArray)

It should be noted that since you're using the API to modify the scene graph, there is no undo available. To get undo, you'd need to author this as a scripted plugin command.