The yellow and purple trains were RABDe 8/16 for the Zürich-Rapperswil Gold Coast line.
AFAIK they were not prototypes for the NPZ, but rather a separate series.
The NPZ were built a year or two later and unlike the earlier RBe 4/4, the motor unit was developed with only a cab at one end.
Unlike the RABe 12/12 (Mirage), the New Pendelzug was designed as a RBDe 4/4 and ABt pilot coach.
There were four prototypes of the NPZ units, each one was painted in a slightly different colour.
The first one was light green and dark green with red doors
The second one was light green and dark green with a red front and red doors
The third one was off-white with a blue band with red front and red doors
The fourth one was off-white with a blue band with a white front and yellow doors
SBB users were invited to vote for their favorite design and the third design was chosen, albeit a decision was made to paint the doors yellow.
Over time, the design mutated (2nd Series) and the blue band widened at the front and rear of the unit, which also became the standard livery for the RBe 540 and corresponding pilot coaches.
This is what the second series looked like: https://fr.wikipedia.org/wiki/RBDe_560#/media/Fichier:SBB_RBDe_560_109.jpg
This was the first 2100: http://www.railfaneurope.net/pix/ch/SBB_CFF_FFS/electric/emu/RBDe560/green/SBB_RBDe44_2100.jpg
This was the second 2101: http://www.railfaneurope.net/pix/ch/SBB_CFF_FFS/electric/emu/RBDe560/green/SBB_RBDe44_2101.jpg
This was the third 2103: http://www.polier.ch/images/archiv/Sutter/normal/SBB/10/SBB.10-08/SBB-10-356.jpg
This was the livery of the fourth (2104): http://www.polier.ch/images/archiv/Sutter/normal/SBB/10/SBB.10-08/SBB-10-376.jpg