You would absolutely have the right to challenge an unlawful policy in your workplace, even if it had no direct impact on you. As an employee of the company, you have the right to argue that it indirectly impacts you.
Or do you personally have to be black, or a member of a minority Ethnic group to challenge racism where you see it?
You can only make a claim for direct or indirect discrimination if you are yourself affected, however you do not necessarily have to have the protected characteristic yourself. You can be discriminated against because someone perceives you to have a particular protected characteristic even if you don't. You can also be discriminated against 'by association' - e.g. if you are using the mask exemption for those who are accompanying or assisting someone who relies on lipreading and you are refused entry. This would still be disability discrimination even if it wasn't you who had the disability, but the person you were assisting.
You can make a claim for harassment in relation to a protected characteristic whether or not you share the protected characteristic yourself. This is not the same law as criminal harassment (usually related to stalking). The EA says that harassment is prohibited conduct and defines it as any unwanted conduct related to a protected characteristic that has the purpose or effect of violating your dignity, or creating an intimidating, hostile, degrading, humiliating or offensive environment for you.
Example from the statutory code: A shopkeeper racially abuses a black customer. As a result of the racial abuse, a white customer is offended and could bring a claim of racial harassment.
Also of course, anybody can write a letter of complaint whether they are directly affected or not. Most reputable businesses, if shown that they are acting unlawfully, will want to amend their practices to avoid the danger of future litigation.