The WOLF is 100% correct. In todays world the color of the shirt means nothing. I went through the Yeshivah system and I know plenty black hat white shirt whatever guys who need that uniform like a luch in kup. Instead I would look more at other factors like
Yarmulka size- I think it says something about ones Yiras Shomayim
Neatness- If the guy looks shlumpy he doesnt respect himself and isnt such a mentsch.
How he carries himself. Is he arrogant, self absorbed, condescending, rude…?
The true litmus test for a guys frumkiet in my opinion is as follows:
Find out his shul manners.
If he davens with Kavannah and doesnt talk by davening, in all likelihood the guys is gold. If he respects the shul, his fellow daveners, and takes Davening seriously it means he has Emunah and a deep connection to Hashem. Usually the daveners and those who wont talk by Davening are much frummer and more “REAL” about their Yiddishkiet.
If you can get this info on a guy it will save you hours of senseless shidduch calls.
Im sure most of the guys will agree with me, but again, a lot of “frum” people talk by davening so they wont like what I am saying. However if you are honest you will agree that the Modern Orthodox looking guy without the hat that Davens the long Shemoneh Esrei and listens quietly to krias Hatorah is probably a lot frummer than the Yeshivish looking guy who talks through most of Davening and Krias Hatorah.