The size of the array determines how the colors are applied to the entity: 1 byte per vertex is applied as a modulation factor (0-255) to the System.Drawing.Color of the entity. This requires the use of shaders so the graphics acceleration must be turned on, devDept.Eyeshot.ViewportLayout.UseShaders must be true (Winforms Eyeshot control only) and the devDept.Eyeshot.ViewportLayout.DisplayMode must be devDept.Eyeshot.displayType.Rendered 3 bytes per vertex are applied as RGB colors 4 bytes per vertex are applied as RGBA colors (in order for the alpha transparency to work, the entity must also have a System.Drawing.Color with alpha < 255 and AccurateTransparency must be set to false).

Reference

FastPointCloud Class
FastPointCloud Members