Here is a list of the aqueous transition metal ions and their colours, that you need to know for AQA and OCR A-level chemistry.
To remember the oxidation states, notice that all 2+ and 3+ ions have no oxygen. All ions with oxidation states of 4+ or greater need oxygen to help them achieve the high formal oxidation states of the central metal ion.
I have included the totally stupid ways how I remember them. The dafter methods are, the more you will remember them (I promise!). I am so used to the oxidising agents dichromate(VI), Cr3+, manganate(VII) and Mn2+ ions, that I don’t need to have a way to remember them. I hope you don’t either, as you have used them loads when doing the oxidation reactions of alcohols to aldehydes/ketones, and aldehydes to carboxylic acids.