the idea is that there are no words that rhyme with purple, silver, and orange.
orange is technically pronounced Or-ANj, but quite often gets slurred in pronunciation to orEnge or orInge. in which case it can be rhymed with door hinge, poor hinge, floor hinge, more hinge, etc.
purple is supposed to have the second p and the l blend directly together, but many people add a very light vowel sound of i or u, creating a purpill or purpull sound, which can be rhymed with sir bill, fur pull, her pull, her fill, etc
silver has a few close rhymes, like still verb, sylph her, but nothing really exact, even with slurring.
Still, when orange purple and silver were listed as words without rhyming words, I believe they meant no other single word, which would exclude door hinge as well as all of my suggestions since they all use two words.