What does the colour tell you?

A primary alcohol can oxidise to an aldehyde, then a carboxylic acid. Distilling off the aldehyde helps limit further oxidation; reflux with excess oxidant favours the acid. Secondary alcohols form ketones; tertiary alcohols resist oxidation under these usual test conditions.

Acidified dichromate changes orange to green when reduced; acidified permanganate typically changes purple to nearly colourless Mn²⁺. Both primary and secondary alcohols can give a positive oxidation test, so colour alone does not distinguish those two classes.

Alkenes rapidly decolourise bromine water by addition in the usual classroom test. Alkanes do not do so rapidly without UV. Complete combustion of a hydrocarbon or alcohol produces CO₂ and H₂O when oxygen is sufficient.