we have preferences indeed, but self control is a fruit to be very much exercised. and the foundation of how much we would go into "prefering black girls or white girls or black boys or white boys (for opposite sex)", should be STRICTLY scriptual. we do not look at a woman to lust after in our minds, for that will be sinning.
but most importantly relationships are not things you go in and out of as you please really. they can be a total waste of time, a distraction to your priorities and can sever your relationship with GOD.
seek ye GODS kingdom first and its righteous and other things such as marriage, finances etc will be added unto you.
i have been in over 3 relationships and each proved a problem to my relationship with GOD. i believe you can learn that there s a big risk when you do this.
Focus on GOD eitherway sis, worry not if the "Good guys" will be taken when you age, GOD knows everyman on earth, and knows "the MAN" for you. either black or white, so worry not on it, neither take thought for it. JESUS CHRIST is what matters.