Is there a difference in usage for λευκό and άσπρο?
I understand that λευκό and άσπρο both mean white, but is there any differences to the context in which they are used?
Yes. λευκός is a bit more literary and aside from a few set uses, isn't really used in everyday speech. The main set uses are for wine (λευκό κρασί) and buildings/place names (eg Λευκά Όρη, Λευκός Πύργος).
For everyday speech, άσπρος is what you're after.
I want to add that everyone has their own prefered words to use. Λευκός does not fall in the same category as some other truly fossile words used only in fossile phrases. Someone can prefer λευκός over άσπρος and use it more. It is true that most people use άσπρος more, though, without that meaning that they never use λευκός in everyday speech.
Πουκάμισο (button down shirt) comes to mind as an everyday item that's frequently matched with "λευκό". Fabrics in general come to think of it...
Tongue-twister for you stellar greek-learners, to sharpen your pronunciation:
Άσπρη πέτρα ξέξασπρη, κι απ'τον ήλιο ξεξασπρότερη!
(ξέξασπρη is like whiter than white or sth)
"Λευκό κρασί" isn't really a set phrase though... Many people, myself included, just say άσπρο κρασί - sounds fine! I think the only real restriction is like you said in places' names - you can't say Άσπρος Πύργος in any case. Another common one is Λευκός Οίκος (the White House).
Also, it seems they're not interchangeable in compound words, a couple that come to mind are ασπρόμαυρο (black and white) and γαλανόλευκη (blue and white - that's what our national flag is called).
I've found another interesting discussion on this here: https://forum.wordreference.com/threads/what-is-the-difference-between-άσπρο-and-λευκό.2469790/
It more or less reflects what's been said here, λευκός being used in a figurative, more formal context, whereas άσπρος being used in an informal, more literal way.
Λευκό is litle more official, more spiritual, more thought provoking etc. It may also mean in some cases clear or unwriten etc. On the other hand ασπρο has to to do more or less only with the colour. I would accosiate λευκό more with the english word "blank" and άσπρο with the word "white". As far as it concerns the wines, I would more than certainly say λευκό κρασί and absolutely not άσπρο κρασί (!). Ι have never heard anyone in my life to say that! If I ever hear it I would consider it just an akward neologism.