Hello Assa.
The stoma belts sound like a good option but there will be no really effective disguise for the bag when in the nude. I like the concept of just decorating the bags that are already used, or purchasing one of the many decorative covers on the market.
My first thoughts on this is that for some people, nudity itself might seem offensive, so why would nudists be offended by a bag? That aside, my next thoughts would depend upon precisely where the bag is situated; If it was more or less were other stomas are, then I might design a belt (and bag) that was disguised as a money pouch; If it was further down, then I would be more inclined towards a sporren (without the kilt).
I think with these sort of issues, it comes down to a matter of taste, personality, robustness of determination and ability to marshall one's potential responses to potential objections. I have found the naturist community to be pretty well suited to these aspects when it comes to nudity, and I would expect that sort of attitude to extend to other aspects of their lives.
However, also in my experience, there are always one or two people who feel they have some sort of right to express their opinions and belitttle others when they appear to be 'different'. I view these people as 'bullies', in that they wish to impose their views on others and have those others conform to what they are dictating. Fortunately, I have studied the concept of 'Bullying' for many years, and have an arsenal of responses to counter any bullying that I encounter, both on behalf of myself and others. I have never been shy in responding to bullies in whatever form they come, so when it comes to 'fashion', I find that certain people are inclined to criticise whatever I wear, partly because it is mostly for comfort, rather than looks, and partly because I have a tendency to make some of my own clothes to suit my needs, so they look 'different'.
Most of the time my response to 'criticism' is to retort that 'I am starting a new fashion'. Some of the things I have designed have been recieved so well that people want to place orders for those items. I view people's resonses to clothing in much the same way as their responses to rhyming verse, in that some folks might like it and others not. Those who take offence and to want to engage in hostility, often find themselves playing a 'game' in which their opponent is not willing to adopt the role of 'victim'. I like to think that I 'educate' people into understanding their own behaviours a little better than they might have done if they had picked on someone less emotionally robust.
Enough of this - for now.
Enjoy you naturism and stand up for what you think is right for you.
Best wishes
Bill