What's the best approach for adding large numbers of values to a custom list CSV, especially if some already exist in the list? For instance "blue" might already exist and we don't want another Blue. I don't believe there is a way to pull a search for custom list values, is there?

do you have ODBC access?

Nope. I've just been given a list.

There's a saved search for custom lists. Just go to the custom list then click search in the upper right corner of the screen. Or just click the excel icon on the list view of the custom list values

I do not see that. I only see Copy to Account.

Convert the list into a custom record it’s much better and easier to work with