All of the frosting must be collected, but two pieces of them are surrounded by liquorice shells and require the double colour bomb combination to collect.
In fact, due to the isolated liquorice shells, the player is required to make an extra double colour bomb combination to open them all.
On mobile due to the liquorice shell mechanic, it is not possible to fully utilize the given colour bombs.
With four colours, it is easy to create special candies to create combinations and collect the blockers.