Bromophenol blue turns yellow - during making SDS-PAGE sample buffer (Jun/16/2010 )

I've never had this problem before and I have previously made SDS-PAGE buffer without any problem but I don't why today when I was making the buffer it turned yellow. It doesn't matter if I first add SDS or glycerol or whatever, it just turns yellow anyway.

I even used another container of Bromphenol blue but it had the same problem

It's a problem in your buffer

Bromophenol blue is an acid-base indicator its useful range lies between pH 3.0 and 4.6. It changes from yellow at pH 3.0 to purple at pH 4.6; this reaction is reversible. Bromophenol blue is structurally related to phenolphthalein-a popular indicator.

http://en.wikipedia.org/wiki/Bromophenol_blue