Colours of the halogens:
All halogen ions (Cl-, Br-, I-) are colourless.
Fluorine (F2) - Pale yellow
Chlorine (Cl2) - Green
Bromine (Br2) - Orange
Iodine (I2) - Brown
F2 is the strongest reducing agent because it is the most reactive and 'wants' to be F- ions more than the other halogens.
F2 is able to displace any other halide ion from solution.
F2 + 2NaBr --> 2NaF + Br2
(F atoms) (Br- ions) (F- ions) (Br atoms)
Pale yellow Orange