Welcome, Wiley, to TFP!
I have the Noche travertine which is a light medium color. If I remember, walnut is lighter. I lived with mine unsealed for almost 2 years before deciding to seal it with an enhancer sealer. We put down just 1 coat. I love the results for highlighting the colors and patterns. A wet deck should give you a feel for what it will look like with an enhancer. It's only been a few months, but it beads up beautifully. Probably next year, we'll do 2 coats if it needs another application.
I was concerned about it being more slippery - I'm old and don't want to fall! Lol!!! I can't tell a difference between before and after. I did not add anything for grip. I've heard mixed reviews on those additives. It's definitely not as 'grippy' as exposed aggregate or rougher concrete pavers. I rarely have children around to share any experience with kids running, etc. You can do a search for TFP posts about grippers (and anything) in the search bar at the top of this page. Also, search on Google.
This is what I used. I liked the reviews, and a member on TFP had used it with good results. It was easy to apply and went far. Aqua Mix Enrich N Seal.
Custom Building Products Aqua Mix Enrich Seal 24 oz. Penetrating Sealer-AMES24Z - The Home Depot
Dry Treat is probably the best stone sealer out there. You have to add an enhancer to it - I'm not sure how that works. It's expensive but has a great warranty. I couldn't afford to use the certified technicians to get the warranty. Also, they want a 21 day cure time, which I don't have.
I have before and after pictures of my travertine on some post, but I can't remember which thread. I still haven't recovered from the PhotoBucket mess, so I can't post pictures. If I find them, I will send you the link.
Take care,
Suz
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Never mind.... I just realized even if I could find the post, the photo links are broken and won't show! Duh...... Sorry. You can find before and after pictures across the internet. I was trying to give you a 'real live' example.