Hello everyone  don’t know if anyone can help me. I done a cake and decorated with buttercream roses but then after a few hours I noticed the colour from the buttercream leaked on my cake board anyone know why ?? 

Thank you 

You colorded the icing/roses just before using it most likely and very dark.  Did you cover the cake board with a food safe covering?  Sounds to me like you did not and just the cake even w/o icing would stain it.    The more paste/gel   color used the darker it will get over time and  most likely might leach onto a board.   It takes time for colors to develop and all coloring should be done at least many hours before needing.  Usually one should make it the day before.         

bump