Some posters have decided -illogically- that there is something significant about the location of the red fibers. The location is thought to rule out secondary fiber transfer.
(You'll have to ask those posters to explain the "logic" behind such conclusions)
There are brown fibers on the duct tape, in the paint tote, on the paint brush handle, and in the ligature. These brown fibers cannot be (or at least have not been, as far as we know) sourced.
It would seem that if the location is significant with respect to the red fibers, it must be of equal significance with respect to the brown. That is, if the red fibers are thought to be present due to primary transfer, from PR, then the same "logic" must apply to the brown fibers found in the same locations. They must have been transferred, by primary method, from someone wearing brown.
Of course there is no "logic" involved, as the fibers, red or brown, could easily have been there due to secondary transfer.
Proponents of the "significant location" theory, with respect to red fibers, have painted themselves into a corner. If they want to place PR in the basement the night of the murder, due to red fibers, then they must also accept the presence of a co-conspirator wearing brown. A co-conspirator who is unknown to anyone but the Rs, and has been protected by the Rs.
OTOH, if theorists would like to dismiss the mystery co-conspirator by saying the brown fibers are there from secondary transfer, then they must admit this could be the case for the red fibers as well.
They can't have it both ways. The red fibers can't be "significant" due to their location while the brown unsourced fibers, in the same locations, are insignificant. If the red fibers could not have been left by secondary transfer then it's difficult to see how the brown fibers could. If one wants to draw conclusions from the red fibers, one must draw the same conclusions from the brown fibers.
The most sensible thing of course is to admit that the red fibers could be in those locations due to secondary transfer. e.g., the fiber evidence is inconclusive. This would apply equally to the brown fibers.
I quote, yet again, from the Georgia Bureau of Investigation -
NOTE: The more matching fiber types that exist in a case, the stronger the evidence of association. Remember that fiber matches between two individuals who share the same environment (e.g. live together or drive the same car) are essentially meaningless.
http://dofs.gbi.georgia.gov/trace-evidence