The Yellow and Purple routes are basically the same except at the beginning near Y Felinheli, the yellow route connects to the existing roundabout and is now the preferred option. The reports are still available on the Welsh Government site and there is a YouTube video showing the route past/through the park.
http://www.youtube.com/watch?v=eqHiYbmX4b8 Earlier version including Brown option which was the basis of the Glan Gwna black option both of which used the existing road and impacted less on Glan Gwna, however they need to build a 2+1 road to get the European funding. 2+1 is dual carriage way on alternating sides.
Did a lot of research into this before we purchased our chalet in November, looks likely to go ahead now but is still 5 years away IMHO, biggest impact will be as previously mentioned to the caravans in the 500s.
Glan Gwna did get planning permission to add more caravans behind the Hall connecting up with the top of the park, I am sure they will move the 500s here if the bypass does go ahead using any compensation from the Welsh Government
Regards Jon