It's like a demented Rosetta Stone.
I love it.
(PS: Love the sentences and the language so far. It's fantastic!)
Can this mean that there is a printed orange on the cover of the book? Or does it only mean that there is an actual orange on top of the book?
I think the word "on" could signify either one.
"An orange is on the book?"
Oranĝo estas sur la libro...?
Either way is right. That sounds better to english speakers, but the other way around "on the book is an orange" sounds fine to other languages.
can you adjectify oranĝo to oranĝa so it means the color?
According to https://en.wiktionary.org/wiki/oran%C4%9Da , yes.
"There is an orange on the book."
I think that's the best way to say it in English. It sounds better than starting the sentence with, "On the book..".