Wickr Me, Pushbullet, Cryptokit (if tech savvy only), Signal Private Messenger (can change colours but the grey/white bubbles is an option if not the default, forget, recent ex had his in red :( ), Wire, Element x - are some secret messaging apps that have white/pale grey/grey bubbles but like Signal some of the more popular secret apps allow you to customise colours.
If it was more pale green instead of grey then that opens some more while cancelling out above. Check the apple App Store to see if these are compatible with wife’s phone, some might be android exclusive. If you find one you think is similar download it to see how it can be hidden maybe?
Did you check her games? This year more fake games that are actually chat apps have come out. Also if she has a calculator chat app, like calculator pro, you will need the passcode in order to change the calculator into the message service. Also FB messenger has a secret messenger now, default is blue/light grey but if she uses fb check to see if it could be that, I think you can change bubble colours too, not 100% though.
No doubt she would have noticed you noticing the screen, very suspicious that she left it out and you couldn’t even match the chat screen to any of apps listed. Did you swipe constantly to make sure you saw all screens? I think on newer iPhones you can drop an app by itself on page/screen 6 for example even though all other apps are one the first and second screen. Did you open all folders as well? Similar story, in a folder you can have multiple screens to drop an app, swipe across to make sure.
For dirt cheap you can get a mini motion camera, if your bed head is ornate enough you could fix it there and watch on your phone, I think they look like mini screw heads. Alternatively if you have some cash to burn on this you could get a cute personal AI companion that has a camera feature, like nanny cam, that you can stream live vid on your phone. She might treat it as a boy toy and not look more into it, alternative nanny cams come is so many shapes these days, an option to keep close to her side of the bed.
Stay well rested and alert. Be mindful of your own body language. Set a date for yourself (pick a date for your investigations to stop and a big choice to be made regardless of what you find) for your own mental wellness, this can become an obsessive activity and you don’t want to go crazy over the unknown.
[This message edited by LostInHisFog at 10:08 PM, Wednesday, December 27th]
They can make as many promises as they want, but if they don't put action behind it, it doesn't mean anything.
I edit because I'm fluent in typo & autocorrect hates me.