Not only did I never see this happen on the SNES version but it isn't even supported by the code (their initialisation code is limited to four colours).
As an aside, these (green, yellow, red and purple) are the four main colours with ice as the fifth global colour as well as one palette row for the player, the rest are tied to the current room which may have been the reason only these balloons exist alongside the fact that four is a power of two which is easier to work with than with five.
Though as an aside, the levels which have the balloons do have a local cyan palette which is compatible with them which may have been the inspiration to add a fifth colour for the GBA version.

Also, the YouTube video is broken.

Don't the giant ones sometimes spawn in light blue? Coulda sworn I've seen it in-game...
EDIT:
They definitely do in the GBA one, not sure about SNES.

The balloon with a Shy Guy could be added to a dedicated Shy Guy sheet. Even then, you still can deduce their position because their head should be placed where the square is. However, you're right with the crate, I'll have to add that one later, so should I do the balloon which carries a large spring ball.

The balloons also carry Shy Guys and crates, which don't fit into the 16x16 box. The crate is also held by three balloons instead of one.