On reading this my first reaction was that you may be someone who looks for prejudice, and if none is seen, looks harder, until some trace of it is found. Perhaps that seems unfair, but I happened to encounter two such people today.
It is certainly unrealistic to say, or even suggest, that the personnel of all banks are colour blind, but, in this case, the supervisor who made the decision apparently did not even see you, and made an assessment based on the documents presented by the loan officer, not on your colour.
Your best bet would be to ask for an appointment with the supervisor, and then discuss it with him/her directly. If that still does not work, do not be afraid to demand that you speak to the bank manager.
You could, if these fail, try another bank, but it is likely the next one would ask if you have applied elsewhere so, before going there, you should ask the first manager exactly what they would like to see, and how would you go about meeting that desire/requirement.
Before doing either of these, make copies of your documents and any credit records and have them with you.
You could also ask for a credit bureau report, so that you know exactly what is on it.