Being ginger is not a protected class, so there is no legal restriction on descriminating (so long as you don’t successfully argue that gingers are a race, eg Scottish, but that’s a stretch).
However morally no, you shouldn’t have a say in it. Either way, usually you’ll be dead when the decision is made. Maybe not with kidneys, although with kidneys you tend to know who you’re giving it to - I don’t think anyone just randomly donates a kidney, like you would give blood.