I have exactly the same issue. It is a real problem in daylight. Nighttime is fine, I wonder if there is anything that one can do to improve it?

I had long conversations with Dell about this. They acknowledge the issue but can't offer an (acceptable) solution; - a wireless keyboard defeats the purpose of having a portable laptop, - they could send a technician to replace the keypads on-site but very expansive option! They say it is not a technical issue but a design issue. and as such not covered under warranty. Not sure if this argument 

You have 30 days from shipment to return an unsatisfactory system for any reason -- do so, and purchase a different model with a more suitable keyboard design.

I thought it is 15 days. And also, I have set up the machine now and don't want to take it all off again! Still don't understand why Dell manufactures keyboards like this!?  If they were sold via a normal shopfront (not on line) I would never have bought it!

For new systems in the US and many other places, it's 30 days.  Refurbished systems may have a shorter return period. 

At least in the US, the XPS 13 models are sold at retailers such as Best Buy, etc.

I am wondering if there is some way to turn off the backlight on the keyboard during the day i.e. in bright light? The issue for me is that the letters on the keyboard automatically turn white in daylight and are unreadable?

The F5 function key on your keyboard (at least on my XPS 15) allows you to cycle between various levels of keyboard brightness, including completely off. 

On my XPS this can be done on the F6 key. 

@AlfieTat and @StZill Thank you so much. I should have known that but I think that this does help greatly. It is also the F6 Key on my XPS13. Thanks for this!

have exactly the same issue. returned my xps and bought lenovo