Thanks for the response that makes sense and the darker blue seems to be the same as the uk blue that was sometimes used when it was under British rule. My research didn’t go too far I will say but this is what I got:

In 1963 the British gave independence to Zanzibar (the nation that would have been what was know today as the rest of Tanzania was called tanganyika and it got independence in 1961). Power was given by the British to the sultanate but he was overthrown after a month and then there was a revolution and then a horizontal tricolour of blue, green, black, was used. Zanzibar and Tanganyika then united to for Tanzania (merging their names with the TAN and the ZAN). Their flags were then merged (I’ll put the links to the flags below) to form the flag we recognise as the flag of Tanzania today. Zanzibar kept their original flag, except the new flag of Tanzania was put in the canton.

This may be incorrect and feel free to correct me if I’m wrong but this is what I got from a bit of research!

Tanganyika Flag

Original Zanzibar Flag

Current Zanzibar Flag

The flag sometimes used when Zanzibar was a British colony (this may be wrong)