Why is there a blue and a red float for a FOP on a gravity fed tank?

[Illuminate]

I assumed that the red ball float was for a header tank on the central heating side and the blue ball float was on a cold water storage tank. I thought the reason for this was only to help identify the tank but after finding a lot of cold water storage tanks with a red float, I must be wrong? Can somebody enlighten me? Thanks

 

[ShaunCorbs]

Doesn’t matter just a ball / float old ones we’re normally red but depends on supplier you can get either

 

[Ben-gee]

Tbh I have red/blue/green/orange in my box of bits.