Part I: Luxembourg and Netherlands
The colors of Luxembourg flag are based on the arms of Grand-Duke of Luxembourg, the head of state. Netherlands adopted those colors during the Batavian Republic, inspired by French revolutionary colors and as rejection to orange-white-blue Prince's Flag. In this specific case, the similarity is even worse because they are very near countries, although don't sharing borders.
But this issue is very near to solution: in 2007, the Luxembourg government approved the use of the banner of arms of Grand-Duchy (also used as naval ensign) as civil flag inside Luxembourger territory along with national flag, and someday it can totally supersede Luxembourg tricolor. It's the banner of arms:
This flag is much cooler, and much more relevant to the country, the reasons it has gained popular approval last years.
Part II: Andorra, Chad, Moldova and Romania
Andorra and Moldova at least use to put a coat of arms on it, but it doesn't work that well. Romania used to put their coat of arms, too, but it's a little in disuse. This issue is even more dramatic because Moldova and Romania share borders, so it's harder to know where you're passing to other side of border.
Andorra colors is a French tricolor with white and red changed by Spanish yellow and red, because Andorra is between France and Spain, and the co-princes of Andorra are the president of France and the bishop of Urgell (a Spanish Catholic diocese). It's my proposal to Andorra:
The yellow and red nine stripes (the senyera) is the arms of Catalonia, the Spanish autonomous community nearest Andorra, and where the See of Urgell is located. It's present in Andorra coat of arms (more above). The blue with the two fleurs-de-lis represent French condominium over Andorra. The number of fleur-de-lis represents the curious case of Andorra and its two co-princes.
The current design of Chad flag is inspired by pan-African colors, but with blue instead of green to avoid confusion with Mali (turning it identical to Romania...). My proposal is based on its coat of arms. See:
Moldova flag origin is exactly the flag of neighbor Romania with Moldovan coat of arms. My proposal is based on its coat of arms — a similar, but more complex flag, was yet proposed. My rendition:
I think this flag is easier to be changed. A flag based on Armed Forces flag or the flag of ancient Principality of Moldova are other options, in my opinion.
To Romania, a horizontal tricolor, used before the current vertical flag, can be an option. See:
It's OK, but I can come with a design by myself:
It represents a legend that states that the tricolor is a union of blue and red from Moldavia and blue and yellow from Transylvania. However I think Romania would be last to change its flag.
Part III: Indonesia and Monaco
Both countries has excellent alternatives from their pasts and presents, so I don't know why they insist to keep the issue.
For Indonesia, there's the flag of Majapahit Empire, currently used as naval ensign and naval jack, consisting of nine red and white stripes:
For Monaco, there's other very reasonable flag: the banner of arms of House of Grimaldi (Monaco royal family), used many times unofficially, specially in 17th century, but still present in rare occasions (also unofficially):
This flag is so Monegasque in origin and use that I can't see why it's not used officially.
Part IV: American seals-on-bedsheetMany USA state flags use a seal or a coat of arms on a blue background (see), what make them almost unrecognizable in distance. You can see my proposals to USA states on my blog, and by many other authors at Vexillology Wiki. I highly recommend the visit!
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