I agree that the mixing of the purple sash of the Order of Leopold I and the silver-and-red dress of Queen Maxima are definitely not the best combination.
As for jewels... all is perfect, the Queens and the Princesses are perfectly bejewelled for a State banquet, the setting of Amsterdam Palace's Burgerzaal is splendid... but I can not refrain a small disappointment. A Belgian/Dutch State visit is not a State visit like any other one, it is a very special occasion between two countries whose history and culture are strongly intertwined. Therefore, it would have been the perfect occasion for both Queens to display something special... like the House diamond parure on the Dutch side, or Queen Fabiola's Spanish wedding-gift tiara on the Belgian side...