Yup, I’m Dutch.
“One of your own flags” might be overstating it; The prinsenvlag has, to my knowledge, never seen “official” use by the (current) kingdom of the Netherlands as such.
The republic of the Netherlands was an entity that ceased to be some time before the current state emerged, AFAIK (history isn’t my strong suit) so I think most Dutch historians wouldn’t consider it a flag directly tied to the ‘current’ Dutch state.
Minor nitpick ;)

(from my American POV) I don’t really see a big distinction between “centre-left” and “progressive, slightly right of centre”.
Read more at http://littlegreenfootballs.com/page/301876_Row_after_four_Dutch_MPs_wear_#ghRG4xkDfPx6ZI2m.99

Emphasis on American POV there, really.
The “left” descriptor has a more ‘socialist’ meaning (while for example the PvdA wouldn’t descibe itself as such anymore, many of it’s members still do, and the Socialist Party doesn’t exactly have all that much room to deny the descriptor ;) ) aside from the ‘greenleft’ (translated) party which by now describes itself, for what I gather, as green and progressive, avoiding the term left somewhat. Basically, high emphasis on welfare etc.
Progressivism (which from a US POV could easily be conflated with ‘left’, I understand), on the economic side focuses much less on what you’d call welfare (and believe me, our system is so much more comprehensive and ‘comfortable’ the average US citizen wouldn’t believe it) and more on stuff like education, criminal rehabilitation, attracting high-tech jobs etc.
left would imply more of an income leveling approach (don’t get me wrong, I support subsistence living for anyone - we’ve attained that quite a while back, though) while the ‘centre-right’ approach favours subsistence level guarantees for everyone, but strong incentives to start earning more.
For example, from your American POV you wouldn’t believe the amount of tax credits and even direct government subsidies we get at low income levels (almost all of our health insurance is paid for, leaving maybe $30 a month on the basic policy to pay for by yourself at low income levels, plus a $450 ‘own risk’ per year, so you’ll have to pay that much yourself first before insurance kicks in. that’s it, all care up to totally catastrophic included. then there’s substantial, as in several $100 a month, housing subsidies on already partly government run ‘social housing’, and there’s quite a bit more beyond that).
Now if there’s loads and loads of subsidies like that at really low income levels but they taper off quite quick, instead of being a bit lower at really low levels but tapering more gradually, one might, from the minimum wage@full-time income level, up through to say, double that, only get to keep maybe $0,15 to $0.25 of every dollar more earned under a system the more ‘left’ist parties seem to strive for. especially the SP would make a right mess of this, given the chance (IMO).
Now us ‘centre-right’ types don’t like being conflated with that all that much. I hope you understand ;)
Sorry if it reads like a bit of a mess, giving a concise rundown of our complete socio-economic situation and the political complexities thereof is hard to do in a few paragraphs! The difference is there, and it’s something we can get rather agitated about (from both ends, of course).

Anyway, that blogger: doesn’t appear all that trustworthy. Gut feeling mostly, but it looks like the kind of type around here who wouldn’t mind being misleadingly deceptive in selectively quoting articles and such.
First of all (to stay with something a bit more factual than my gut!), I’d like to point out that while we have racist scum around here, the anti-racists are generally the more violent and dangerous scum. It’s a small group but the hard core is really, really nasty. And they have more than a bit of a habit of just flat-out lying. Sorry, anyone taking them seriously as a source has an instant trustworthiness problem in my eyes. This is not me taking any kind of extreme view: I’m sure just a significant majority at my, very very much mainstream, law school would agree.
Also, the socialisme.nu site she also uses as a source is seriously dubious, and she has a habit of using highly, highly partisan sources.
I could investigate further if you really want but just by what I’ve seen from her sourcing (and there’s more I just really haven’t got the time to type up) she’s just not a reliable source. Highly, highly partisan and any facts she’d state I would look up in reliable sources, before trying to argue them as true, tbh. `

I’d also mention that while proving a negative would take some more time than I have right now, the volkskrant, basically a rather left-leaning, pretty anti-PVV oriented but generally reliable even if somewhat partisan ‘large’ ‘mainstream’ newspaper hasn’t got a peep on this.
Believe me, if something as outrageous as this was actually what that blog is making it out to be, the volkskrant would be __all__ over it. In fact, any newspaper around here probably would. They’re not, and this is something that would certainly generate a lot of sales.
Not saying this proves it isn’t true, but I’d be deeply suspicious of that blog at the very least.

Hope that helps :)