I think that this is a tricky question to answer and certainly no string maker that I know of describes their stings as bland or neutral (which is just what you’re looking for). It struck me that D'Addario do rate their string range for brightness and mellowness so if you chose something in the middle of their range then you’d likely be getting something that was towards neutral. As I read their website clear n ylon seems to be their middle ground and IIRC you’ve already tried the similar Ernie Ball clear nylon strings ... I’m wondering what you thought of them ‘cause I’m considering trying them out on my CK35.
Someone mentioned Aquila, I like their Super Nylgut strings but don’t much like New Nylgut (to my ears they are subtly different). You might find that New Nylgut is near neutral and reasonably loud.
Edit. As in the comment below mine - and I believe that there is some validity in the belief - some folk say that Nylgut strung Ukes sound all the same, that the string dominates the Uke. However, IIRC, Ken Timms used to string his Martin replicas with Nylguts and his Ukes still sounded great so string domination doesn’t always happen.