Yes well, with Timbouctou blocked by the admins we may actually do so.
I find your claims very possible, but again, what is required are reliable sources, not claims. Even if we assume you are correct in that this was the "first" flag used after the HDZ came to power, this is not what we're looking for. What we are looking for is the flag that was predominantly in (official) use. I.e. even if the white-square-flag was used the first time, which I admit was likely the case, that does not necessarily mean that it is the version of the flag that was used afterwards in any significant measure - particularly since the Croatian government very soon afterward adopted an official flag with the red-square-first chequy (to distance itself from Ustase symbolism).

To be perfectly frank, the lack of sources here makes discussion very arbitrary and difficult. I mean who really knows which version was more commonly used? And I understand there probably are no sources on this. However, the WP:BURDEN of evidence lies with the editor who introduced the disputed changes, i.e. yourself. So I really don't know what to do other than to again ask you whether you have some real reliable sources that support your edit?  (TALK)