I'm gonna disagree with the esteemed SteveF here; I reckon if they're Puritan witch-hunters, you don't really have much choice. Black, white, and brown are what you've got to work with. Puritans really weren't into display, the really extreme ones (such as might become witch-hunters) considered colourful cloth sinful. Actually sinful, as an expression of Pride. They be likely to burn people in colourful clothes (especially badass fictional witch-hunters). You might get the odd dark red or dark green doublet-type thing, but I reckon in general you're looking at sombre colours.
If they're the Holy Inquisition, however, you have more choices. High ranking Catholics have traditionally favoured red or that wine-purple colour bishops wear. Or you could have a bunch of crusading monks in a variety of different robes and hoods - white, black, black and white, grey, brown...