Verdict: False
Contrary to popular belief, this really is a myth. Concealer should closely match your skin tone or foundation in order to effectively conceal imperfections. Using a concealer lighter than your skin tone or foundation will only draw attention to what you are trying to cover up - more importantly, it will look ridiculous.
Now, if you are reaching for a lighter concealer because you have a bad case of dark circles, you may want to add a colour corrector into your makeup routine. Applying a colour corrector underneath your concealer will help to neutralise discolouration and improve your complexion. Peachy or orangey colour correctors are the best shades to use as they counteract that nasty blue/purple tinge. However it is important to know that different colour correctors suit different skin tones, so you'll need to make sure you find the right one for you. Very fair skins should pick a salmon colour. Those with olive skin should pick a peachy colour and those with dark skin should pick an orange colour.
If you don't feel comfortable venturing into the world of colour correctors just yet, I would recommend using an illuminating concealer - it will cover your dark circles and brighten the eye area. If all else fails, get your hands on the Stila Brighten & Correct Concealer 30ml (£18.00 beautybay.com / $28.00 amazon.com). It is a foolproof, multipurpose must-have that conceals, corrects and brightens.