changing colour of front dye in sds-page - (Sep/23/2009 )
I'm not sure if anyone is still interested, but I noticed a reason why sometimes gels would do this in specific areas but not others.
I just ran a native gel (bio-rad), and I noticed some parts of my gel stopped running and are turning yellow too.
As the gel runs, bubbles build up on the bottom where the tank feeds buffer into the gel.
If the bubbles get big enough and block a decent area of the slit, my hypothesis is that it can prevent the buffer from feeding ions into the gels, thus dropping the ph.
Easy fix when this is the case is to just tilt and shake out the bubbles before they get too big. The front turned blue again after a while, but I didn't figure out the bubbles fast enough so my gel is sill not straight.
Hope this helps someone maybe.