In battle mega-evolutions take their shiny colors from the non-mega shiny sprites so if the mega-evolution uses different colors than the non-mega the shiny doesn't appear in battle. Some cases where this is a problem would be mega charizard x, mega gengar, and quite a few others.
In battle mega-evolutions take their shiny colors from the non-mega shiny sprites so if the mega-evolution uses different colors than the non-mega the shiny doesn't appear in battle. Some cases where this is a problem would be mega charizard x, mega gengar, and quite a few others.