In regards to your beach towel...i would like to offer you a simple solution rather then saying its a incorrect beach towel of Boba Fett. That and could be a good conversation piece for you, if you want that is.
I did some research on the history of Boba and other Mandalorians known to date with what sources i could gather. To my knowledge until just yesterday, there is no record of a Mandalorian with grey armor. Then i realized the answer was right under my nose, the source i needed to look at was the very book i was reading...Bloodlines.
A former clone trooper and now merc/bounty hunter sporting Mando Armor has a all grey variation of this suit. If you havent read the book then this next part will either make you think im a liar or i just typoed. But the clones age is 140 years old. His name is Skirata. From the words of Jango Fett himself, this is how he described Skirata...
" A short, tough, fanatical man who trained clone commandos and was the dirtiest fighter i have ever known. "
Well just thought i would say my 2 cents, hope i could help in any way. Or maybe i was just useful in wasting some peoples time in writing this. Either way, this is what i found.