Ask Mr. Smarty Plants

You are right that Danaus plexippus (Monarch) butterfly eggs are not orange—they are white.  The eggs of the other closely related butterflies that feed on milkweed plants [Danaus gilippus (Queen) and Danaus eresimus (Soldier)] are also white.

A possible identification for the orange eggs is Labidomera clivicollis (Swamp milkweed leaf beetle).  You can read more about the beetles from TexasButterflyRanch.com.  You can see from the map on the TexasEnto page that their range includes Massachusetts.  If that is what the eggs are, you might want to get rid of them if their larvae are seriously defoliating the plant.  Of course, you can't use a pesticide to remove them since that would also impact the monarch, queen or soldier butterflies.  However, you should be able to handpick them to remove them.

Here is a photo guide from MonarchWatch to 26 of the more than 100 species of milkweed plants and here is a link to the 62 native species of the Family Asclepidaceae (Milkweed Family) listed in our Native Plant Database.  You don't say which of the milkweeds you have in your garden; but, if you don't know the species, perhaps you can find it in the MonarchWatch guide and/or in the list from our Native Plant Database.