I selected the irises in an existing eye texture file (the light blue) that I loaded into GIMP, and then use the "Colorize" tool--pretty simple. The eyes might be a little brighter than realistic violet eyes (say, like Elizabeth Taylor's), but that's what I wanted for the picture I'm making. To use this material, create a "materials" folder in "v1/data/eyes", and drop in these three files. EDIT 7/6/2016: The thumbnail wasn't displaying, due to a filename issue; corrected now. EDIT: attached to the corresponding asset.