Editing the visual appearance of the volume...
Open a volume data set of your choice, then press ALT-V or select Volume Editor from the Editor menu. The volume editor window pops up. Select the transfer function tab.
The transfer function is used to assign visual properties (color and opacity) to the voxels of the volume data set. In the transfer function window, the transfer function is displayed as four different curves (for Red, Green, Blue and Alpha). In the diagram, the x-axis represents the scalar value of a voxels. The corresponding value of the color component is displayed on the y-axis.

Make sure that all the check boxes are cleared, except the one for the alpha component. Now you edit the opacity of the volume. Use the left mouse button in the editor window to paint the alpha channel. You can use to left mouse button to draw piecewise linear strokes.
Now select the color components and try to assign unique colors to the different parts contained in the data set. Transfer function design is a time-consuming process and requires some experience. Take your time to experiment with different settings!

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