bands becoming wavy with colour of the dye changing to yellow - (Apr/07/2016 )

hi,

As the bands reach 1/4th lenth from the bottom of the plate a curve appears on the gel and the colour of the stain changes to yellow. repeated the experiment several times changing the voltage and buffer. please help 

assuming the tracking dye is bromphenol blue, it turns yellow at low pH. the tracking dye passed through an ionic front migrating through the gel (often due to components in sample's buffer). sometimes it will turn back to blue if you run the gel longer.