While it is true that there are no "rules" in this regard, only matters of opinion, it is also true to that the OP posted on here asking for people's opinions. So let's help him out with our opinions.

Yes, you will see A LOT of men at formal functions wearing their Prince Charlies with white or ecru (cream) colored hose, and no, it does not necessarily look bad. You'll even see Prince Charlie jackets advertised from some of the major Highland dress manufacturers and suppliers worn by models wearing white hose.

So why do a lot of people also have such a negative reaction to the idea? A few reasons:
1) The bright white color really looks glaring on some people's legs and to my eye can unbalance an outfit.
2) They are SO common, and with so many different colors in the rainbow why do you want to pick the same color hose as everyone else (and a relatively boring one at that)?
3) Historically diced or argyle hose were the proper thing for evening wear, and while they are less common now, it seems somehow incongruous with tradition to have this style replaced by the simplest, plainest option.

My advice for you would be this -- wear your best pair of hose. If that is your ecru hose, then so be it. You'll probably look and feel ten times better in a pair of real quality ecru hose than in a pair of real cheap navy hose.

My further advice would be that if you find yourself attending a lot of formal functions and getting a lot of wear out of your Prince Charlie, it might be worth investing in some diced or argyle hose. You'll get a lot of use out of them and feel like a million bucks at your next formal occasion.