The CRC has got it right
most people are under the mistaken belief that colour determines kashruth of beer but many things can make a beer dark
and flavourings can be found (but labelled in a world of allergies) in lighter beers
you can stick to the declining sales of ntional macro-brands, and are missing out on flavour. The macro brands put money into advertising rather than ingrediants, beginning in the late sixties.
In almost every case, I have either contacted the brewers directly through their site or read a full description of the beer at http://www.ratebeer.com
A head of a major kashruth organization has told me I can do that, and recently, even in a case where a tiny amount of say raisins was added to the vat
BTW, He’brew Brewing (not a joke) has KSA hechsher on complex dark beers