Trying to displace iron from ferrous sulphate heptahydrate using aluminium foil but nothing has happened
You are correct: Commercially available metal foil is typically made from aluminum, even if it's commonly called 'tinfoil' sometimes. As you say, technically, tin foil is made of tin; aluminum foil is made of aluminum.

Jannis Andreska is also correct: The passivating oxide on the aluminum is likely preventing the iron ions from reaching the $\ce{Al^0}$ and swiping their electrons.

So, you are correct again: The yellow/orange color you're observing is probably oxidation of the $\ce{Fe^{2+}}$ to $\ce{Fe^{3+}}$, by $\ce{O2}$ in the air.



One possible approach to breaking the oxide would be to connect the foil to the negative terminal of, say, a AA battery, with the positive terminal connected to a junk stainless steel spoon, also submerged.  That might not be enough voltage to break down the oxide film, though; on the other hand, a higher voltage might lead to corrosion of the spoon and the release of iron and other metals into your solution.  May or may not be a problem for your experiment?

Regardless, I would recommend adding some table salt $\left(\ce{NaCl}\right)$ to your solution, both to increase its conductivity and also to introduce chloride, which may help to attack the oxide on the aluminum, in tandem with the applied potential.