When you construct a static list of values with LIST expression, it does not matter if you enclose the list items with double quotes or not, as AppSheet interprets the list items as text already. So below expressions are truly identical:
LIST(Red, Yellow, Green) === LIST("Red", "Yellow", "Green")
However, when replying to a post of @Kirk_Masden, I have realized something which seems a bug to me. When you use such a LIST expression in-conjuction with other expressions like FIND, appsheet evaluates the above 2 syntax differently. For example:
 FIND("Red", CONCATENATE(LIST("Red", "Yellow", "Green")))
 FIND("Red", CONCATENATE(LIST(Red, Yellow, Green)))
The first expression evaluates correctly and returns the value of 1, which is correct because the item “Red” starts at the 1st index of the string. However, when evaluating the second one, the very 1st item of the list is capitalized as RED and as there is no match, the evaluation returns the value of 0. Provided you explicitly capitalize your search string in the second expression, it returns the correct value as 1.
FIND("RED", CONCATENATE(LIST(Red, Yellow, Green)))
Here is the screenshot from the expression tester: