Texas police need to be able to clearly see your vehicle license plate at all times. You can add a frame around it if you like, but don’t put a filter over it, or any sort of cover which might make it difficult for police to clearly read it or you will be afoul of the law.
Texas Department of Motor Vehicles is very clear on this point at their web site:
What does “law enforcement legibility” and “reflectivity” mean?
Legibility is the ease in which law enforcement may clearly read a plate’s letters and numbers.
Reflectivity allows the plate to be seen from long distances at night and is helpful in locating vehicles at night or off roads.
There is also a state law which requires Texas drivers to be certain their license is clearly visible at all times. That means your license plate light needs to be functional and bright enough to completely illuminate your license plate at night.
If you violate these orders you run the risk of receiving a vehicle citation from an unhappy police officer. She will be unhappy because having a visible license is not only the law, it’s a way of keeping you and your vehicle safe.