Vector Image from tensor2metric -vec structure RGB

Dear Mrtrix members/experts,
for ROI drawing I would like to open the color coded FA image from

tensor2metric -vec

. But in slicer because of all the available tools for ROI.
But i don’t really understand the way it is displayed in mrview, the first volume is RGB but has only one voxel value instead of 3 in the voxel informations. so i tried to extract separatly the 3 colors to reconstruct a 4D volume and the result in a bit different.
So my question does each volume corresponds to 1 color from RGB ?