Well...there are a couple of ways you can get around this.
If you are knowledgeable with modifying bin files you can change the string to point to the white texture on the
three files concerned.
Find and change this line: <BlueprintID d:type="cDeltaString">RailVehicles\Freight\HS-Cylindrical\Shared\Numbers\
Digits_yellow.xml</BlueprintID>
To this: <BlueprintID d:type="cDeltaString">RailVehicles\Freight\HS-Cylindrical\Shared\Numbers\
Digits_prr-wh.xml</BlueprintID>
Okay, you will have white numbers instead of yellow....better than grey bars.
The other option is you can create your own textures as what I did ( pic below ). I use these for my own use and have no intention of uploading, therefore did not have to ask for permission from Michael ( GreatNortherner ) to modify existing textures or from Amtrack505 to modify his work .
hc_hopp.jpg