As mentioned above; any colors are fine (even mixing in a red for a Parliamentarian).
That said, historically, bright dyes were expensive (a nice red very much so, and black exceedingly so). Thus, just going with a rough rule of thumb here, using red for some officers (gentlemen/lord types) would be good. White shows "purity", by some definitions as well. [Remember Cyraneo's comment about his "white plume". ;-)]
Certainly, there was not "official/uniform" color for this from regiment to regiment, but as also pointed out, a unit could (rarely) have a colonel that decided "all my men will wear…" and would have purchased it for them (that said, evidence of this is very, very little, and nothing that I have found in the ECW).
Regular troops (infantry, horse, etc.) should not wear plumes. Any so-called feathers they might (a big might) sport in a cap or hat, would be of the local variety, such as pheasant, etc., if that is, they could get ahold of one.
Remember, battles and campaigns are an awful affair on clothing and kit, so fancy things like plumes would be rough handled pretty quickly. Not to mention, rain (and ol' Blighty was/is wet!) does a number of plumes as well. Heck, just from my re-enacting days, I had a "rain hat" with nasty old rained-on plumes, and saved my nicer one for dry weather, so I didn't have to keep spending money on them!
Anyway, just my few tuppence here.
Regards,
Bob Giglio