here is another screenshot illustrating the issue:

Looks like a feature to me.

@Malqua The one in that pic doesn't look square to me. :P

Here are some more real world examples:

Maybe the special Tropicraft sands could generate as whole islands with specific sand colors rather than single chunks filled with them.

It was a joke. The real world also isn't rendered in chunks.

They want to make the type of sand biome specific, but it's not implemented yet. The piece of code dealing with that is currently in the replaceBlocksForBiome method of the ChunkProviderTropicraft class, but should be moved to the biome generation instead, according to the comment accompanying the said method:
public void replaceBlocksForBiome(int x, int z, Block[] blocks, byte[] metas, BiomeGenBase[] biomes) //TODO: Move to biomes

For now and upcoming releases, these sands will be used as a supplement to existing gen features like coral and seaweed. For now, there will not be different types of sand beaches, but we're not ruling it out for the future.